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So we don't have the actual codex, but if you're following the hype train we know what is mostly going to be in it.
This is essentially my idea, have a tallarn warlord for the flank stratagem and a catachan detachment for the 1D6 reroll for heavy weapons. We know the shadowsword wont lose anything when it moves, so I take the 1D6 reroll for it to really dish out some vehicle kills. The plan is to drop that unit of punishers, a chimera, and psyker right on the enemy turn one using the tallarn stratagem.
As needed, the shadowsword could be flanked instead of the psyker. However I've had the best luck using psykers to deny on my flanks with marines, so I assume this list is no different.

Does anyone have any suggestions?
Points calculated are using the new values.

Tallarn Battalion

HQ
Primaris Psyker
Primaris Psyker

Troop
Inf Squad (10)
Inf Squad (10)
Inf Squad (10)

Elite
Commisar

Heavy
Leman Russ Punisher (x3)

Transport
Chimera (for long range op sec missions)

Catachan Spearhead

HQ
Primaris Psyker

Heavy
Leman Russ Battle Tank (2)
Leman Russ Battle Tank
Leman Russ Battle Tank

Catachan Aux Heavy
Shadowsword

I love the leman russ battle tanks coming down in price a bit. I will definitely be rocking some. But your army looks like fodder for a deep strike plasma / melta heavy list. Infantry squads would do better with more orders issued. I'd be scared to face a tempest scion list here. Regardless, looks very fun. What do you face most locally? Often think about them more than you, or just play what looks the coolest and make it work!!!