I've been doing some thinking concerning alternating activations as well.
Short rundown:
Player's simply take turns activating a unit (no bidding or anything of that sort, very simple) until every unit has been acitvated. When activated, the unit goes through the phases per usual,
only that the morale phase happens after every unit has been activated and is again, taken in turn by the players.
CHARACTERS have a special ability, to be activated at the same time as another friendly unit within 6" unless they have 10 or more wounds. Some units that belong together,
like grot artillery and their respective crews.. You can (usually) never activate more than two units at a time.
Units arriving per deep-strike are always the last units a player can choose to activate.
The player who finished activating all of his units first, gets to start on the next battle round.
Things that make for tricky situations right now are transports and combats with more than two units involved (not counting characters that have been activated alongside one unit).
That was the reason I quite liked the clustering / bidding idea. If you group a few units that you think should act together, you can.
They only issue is that it takes a bit more time to organize, so you might end up activating after your opponent.
In a simpler format (like the one Star Wars Legion uses) your initiative is actually directly based on the number of units you are trying to activate.
But I was thinking that Powerlevel is a slightly more precise mechanism. Not sure yet though.
Just number of units has an elegance as well (for one, simplicity). And it puts a bit of a stop to
MSU tactics (at least, if you want to act quickly with some good firepower).
In case of a tie, one would still roll off.
Legion has a max of about 3 or 4 units in a single activation, which is pretty elegant as well. Problem in
40k is that you can put a lot more units in a transport if you really want to. So that's not gonna translate under all circumstances.
A Stormlord with 18 Heavy Weapon teams in and 2 Characters in it (8 units) would require 10 activations for all of them to do something.
Slight rule modification: You could add a 'Disembark' option upon Transport activation (making disembarkment from a transport a part of the Transports turn/activation, and not part of the disembarked units turn/activation), so they chose models can be ditched on the spot by a transport upon activation, Models using the transport as a fighting platform / gundeck would be able to activate later, but wouldn't be able to disembark after the Transport already moved.
Close combat gets complicated when you have two units trading blows and then a third one charges in. If the assaulted unit survives, does it get to fight back another time?
Good point. I think this can be resolved within the framework though.
That's the reason I added a 'fight back counter'.
Though I didn't include rules about -when- you can fight back. Didn't think that through completely, to be honest.
That should be : Use fightback any one time during a battle round after you were engaged in close combat by an enemy unit that has been activated this battleround (in normal fight phase order). Note: you can use 'fight back' only once per combined battleround.
This means you can choose to wait fighting back until your opponent piles in more units (even in a later activation, or in your own activation), or you can fight back at once in the current enemy activation (using normal fight phase rules like who strikes first).
So if your opponent activates multiple units in one activation and charges with those at the same unit(s), they are all going to fight (as per normal fight phase rules).
But then, what about units with special abilities like daemonettes and banshees? A general problem your and my solution is, that there is always only one active fight going on,
so player's don't swap back and forth activating units in the fight phase, which in turn makes these 'counts as having charged' abilites useless during the first round of combat.
And unless both units in CC get to strike during one of their activations, these abilities will never be of use.
Also good point
Those special abilities for daemonettes, banshees and any Emperors Children unit, alternate when they are being charged anyways. Starting with the unit who's turn (/activation) it is. So one charging unit strikes first and that's that. If there are more, they alternate.
The effect is a lot more effective in a prolonged combat though.
Rule modification:
Units with this trait always fight first in the Fight phase even if they didn’t charge. If the enemy has units that have charged, or that have a similar ability, then alternate choosing units to fight with,starting with the player whose -activation- is taking place.
So if an activation includes multiple units that charge such a 'lightning reflexes'/'formerly strike first' unit, the rule still has an effect.
And two (or more) units are already locked in combat at the start of an activation in which such units are included, that's the moment these strike first abilities work best. In that case the Daemonettes / Banshees etc. strike first, as per normal fight phase rules.
Example:
A unit of 5 Assault Marines and a 3 model Marine Biker unit charge a unit of 15 Daemonettes (after shooting) during their activation.
The Marine player decides to let the Assault Marines strike first. They roll badly and kill 2 Daemonettes.
As the surviving 13 Daemonettes have their special rule, they can choose to strike back next, and are targeting the Bikers as they have yet to strike. They kill 2 Bikers (sorry, Chaos bias).
After that the surviving Biker can strike the Daemonettes, killing 1.
Note that when the Daemonettes are activated, the Daemonettes can fight (unless they fall back from combat, but why would they).
And they will strike first then as they have their special rule.
If the Assault Marines and Bikers didn't already do a Fight Back that turn (probably not, as they wouldnt have been able to charge if they did, usually), they can hit after the Daemonettes.
So I think those 'strike first' rules still come in handy.