With the way the seem to be trying to make AoS 3e as close to 40k 9e as possible, I think it's very, very likely that the modifier cap rumor is true. What is more unclear is whether it's just going to apply to hit/wound modifiers, saves as well, or everything.
Just watched Caleb Hasting's video on the new coherency rules, and this is just a straight up middle finger to melee infantry in the game, which seems to go along with what I'm seeing as AoS wanting to push shooting and mobility as the main playstyle. Except for super-elite, 3-model units, you're only able to get around half your troops into combat even if you're running an MSU of 5 or 10 models. This is *really* going to slow down melee combat and movement in general, but it also in a roundabout way seems to fit with their idea of wanting big, centerpiece models to be better. If you run say a Maw-Krusha into a 40-man horde, only maybe 10-15 of those models are going to be able to actually attack. So the horde will be lucky to get 1 or 2 wounds on the big guy, who will then proceed to wipe out around a third to half the unit. This applies to basically all monsters and big models, as wrapping them with groups of enemies becomes difficult to impossible depending on the terrain and size of the unit they're fighting. I guess this does cement spears or other weapons with 2" range as the superior option 90% of the time...
All of this of course comes with a BIG asterisk saying that a complete re-work of combat in the game might mean that this new rule makes perfect sense within the new framework. So really, we just have to wait a few more weeks and see what happens.
And unfortunately it’s a very easy fix to avoid AoS Lizardmen making the game unhealthy - make Saurus more viable so that they become meta over Skink spam, but for some inexplicable reason GW won’t do it. Pity because until they do I’m not going to use my Lizardman army in AoS, because I’m never going to sink to the low tactic of repeatedly summoning endless hordes of crap skirmish troops so they fill up the board.
From what we're seeing of the new rules, I really think GW wants melee-centric infantry in general to go away. They want MSU of cavalry and blocks of archers/other ranged units bouncing around the board while gods and monsters hunt those small units one at a time, not melee hordes charging into each other. Smaller board sizes and rules encouraging smaller unit sizes, along with rumors of point hikes on everything to decrease army size in general all point to them wanting AoS to move to a much smaller scale.