MP without full features will not please reviewers or fans.
If you go SP-only, then all features of the game have to be done well by the AI, even if it means removing features from the game itself. This was the big flaw in FFH to me, too many things the AI just didn't do well.
I think having full-featured MP is the best option, though that depends on what resources are required for it. It shouldn't be heavily supported though. Maybe listing what would be cut if you did that , so the fanbase could see what the option is, would be for the best.
One idea here: maybe when the game is ready to go out of beta, implement full-featured MP last, or something else, and let the fans vote on it? Then, if a reviewer asks, you can at least say that you responded to the wishes of the fanbase, who preferred x to y. That might save you on the review.
I do like StevenAus ideas of hard-limiting the number of "pulses" in a round of tactical combat. If initiative pulses go over x, the remnants of both armies get stuck , any armies joining the battle afterwards also get stuck, and the next turn starts with that battle continuing. Also any unit that goes adjacent to that square has to either join the battle or stop that turn (ZOC)
Another idea I'd like is for "tactics" in autocombat, you could do something like stall , assassinate (all out assault to kill champions/strongest unit) , or normal (try to win normally) Ogre Battle is a good example of what I'd suggest being implemented.