Mech armies (particularly Mech IG, because rhinos are even less effective assault boats than they were in 5th) are NOT in any way dead - they're not as "autowin" as they used to be. Still, having AV12 presents a solid target to non-gauss weapons that still makes chimeras viable, whereas weaker rhinos have gone back to being moving coffins again. I can see gunline esque mech making a resurgence, as iffy 2d6 charges make it considerably more risky to go in for the burn with a heavy flamer (and my mech wall o'death is out now - i mainly just use it for the screw you factor).
Platoon Command Squads with spammed flamers in chimeras are where should be at in this edition - 4 Templates (5 if you include the transport), which results in 4D3 hits on overwatch - pretty good at crowd control and point defence (i can see this unit cropping up more and more in 6th, probably to cover footslogging platoons). The unit protects the tank and the tank protects the contents - Mixed tactics here.
Heavy support spam lists seem an interesting thought now, with the double FoC at 2k like 18 vendettas (just for the lulz and a screw you to any air/mech lists), or as my signature refers to, 6 manticores. Yes very handy in the "Big guns never tire" mission, and perhaps a great leafblower type option.
Fortunately, as IG already have a broad arsenal in the early stages of 6th (Hydras & Vendettas in addition to artillery), we get to pick allied codices more as per personal preference, rather than to plug glaring gaps in our codex as we transition to 6th. Plus, even as an allied detachment, we can end up forming a HUGE army.
Personally, i think blobs WILL work, because largely it depends on how you use them - if you want an ablative meatshield for your chimera wall (like me, because i'm a shrewd Imperial Guard Commander, but not Chenkov level, yet
), then having a few infantry squads blobbed up is not too bad an idea (means the wall should stay a a little longer and have a greater sprea). If you want stuff to move up the table, then yes maybe a single hatestomp is not so great - particularly if you feel ballsy enough to go for a CC guard list (this has died given the nerf to FC and PWs - IG have limited access to PFs, and most of the PWs available are swords).
Splitting a 40man blob into 2 squads of 20 will be better, but i think going full MSU is still up for debate - One IS is stupendously weak on its own, but 2 is a bit more of a challenge, but still has small enough impact to be similar to MSU.
@Nave senrag - as moving and shooting is done on a model by model basis, you could conga line the unit (if its big enough), to have a heavy weapons battery at the back (which remains static as long as possible), with the rest of the blob moving forward and dakkaing with lasguns (this is more possible with the buff to rapid fire weapons).
Also wanted to add - with the advent of "Our weapons are useless", walkers like the armoured sentinel have lost such a great role - locking down units with a much higher value than the sentinel itself - armies such as nids just need to get themselves out of synapse range to get out of tarpits. Plus the Plascan nerf might mean we see less armoured sentinels overall (WTF?? Power armoured super smurfs get a better chance than a tank to avoid a gun overheating? Matt Ward must have had a field day).