As I’ve said before, imposing a hard cap on the number of actions per turn would just make some types of teams significantly worse while not really hitting the ones that matter. The good setups, for the most part, don’t take all that many actions to win. For example, Letting Infernus cast and having said Infernus getting a single extra turn is pretty much the end of any fight, whereas a finesse loop like Alchemist/Terraxsis has to take several “empty moves” to set up alignment most of the time.
The combo breaker you are speaking of here (spawn streak breaker) is simply an influence and has been repeatedly stated not to take effect until five casts of a spawner getting an extra turn within the same “turn” and not a hard limit. Also, it doesnt prevent just cascading into an extra turn when you clear space with match 3s, which also happens a lot on a stacked board. Since five casts of Elemaugrim ends basically any fight, he is often only subject to the combo breaker at all if it comes the tail end of the fight and you use a troll to prime him. Yasmine is slightly more susceptible needing a few more turns to win. Things like pre-nerf Justice Leauge would barely be influenced as well, because five spawns means one foot in the grave at a point where a miss wouldn’t have mattered. I have long believed the influence starts before the fifth spawner cast, but that could just be the natural progression of RNG, and it still usually isn’t enough to prevent a good setup from closing out the match without giving up the turn.
Anyways, these are good demonstrations of why even this piece of code can’t really perform the function of “prevent team from getting looped to death by methods with spawners” and instead the most it can really do is “slightly mitigate the annoyance on otherwise infinite, ineffective spawn loops that should have never been a thing in the first place”. Careful play to allow extended loops at the cost of it taking much, much longer and allowing a weaker opponent to be able to take out a stronger one should always be on the table.
tl;dr: Looping was never the problem.
If anything, absolutely this. This is the kind of thing begging to be a new mode, and aside from setting up a branch where it can have differing core mechanics, should have relatively low overhead. Spell chains are something I view to being essential to my enjoyment of the game (I played early iterations of Gems of War where I didn’t have access to any effective spell chains and personally found the pacing to be atrocious), but I’m still curious. More than likely, though, this too would be dominated by exploders spam, because exploders need the least amount of “extra actions per turn” to be in a position of strong advantage and I’ve trivially brute forced my way through a number of battles with exploders even if the other team took a bunch of extra actions and my troops got frozen. Others, though, could be a lot more or a lot less viable (like queen mab being entirely superflous, and barriers being a lot stronger and probably wanting to use dispel to get around them), so it would be interesting to see.