Didn't 5th ed have ambush rules?
One player gets a certain amount of tokens, some tokens are fake, others real.
The blips can move 6'' a turn, but not run shoot or assault.
Either the controlling player can choose to reveal a blipat the start of his movement phase, or they are revealed I think when an enemy unit moved within 12''.
When revealed the units appear exactly as if disembarking from an open topped transport, the blip being the hull (so they could assault).
I don't think the rules ever said what could/couldn't ambush but common sense should prevail
I may just be pulling feth out of my arse though, and I don't remember anything else.
You could do both sides having ambush or either side fiddling points.
Could be interesting in Kill Team and/or with the Zone Mortalis rules.
If you've seen the Ork Kommandos which are just guns poking out of a box or holding up an Ultramarine picture I think they weere originally built as ambush markers before they removed the rules.
The Genestealer blips in space hulk make good markers, perhaps using masking tape or cut down post-its on the bottom to show what's what.