I personally would LOVE Thunderwolf Cavalry. But only as a super expensive separate unlockable unit. Not as a mount. In the tabletop, they're very powerful units but rather expensive and you can't blob them. It's risky but super rewarding. For example, they aren't used as front line assaulters. The key with them is to keep them out of the line of sight of mass ranged fire and get them into a flanking position. Think of them as super mobile Terminators. And please guys, could you imagine the animation for the wolves themselves? If done right it could be gorgeous if it's done naturally and fluidly enough. Also, it's totally viable these giant wolves could withstand punishment within reason. I mean, it's THEIR blood that Space Wolf Initiates have to consume to become true Wolves of Fenris. If there's anything that makes me roll my eyes, its the character Canis Wolfborn...literally Wolf Wolfborn, raised by wolves, rides a wolf...wayyyy too much wolf.
As much as i like the idea, it pains me to say it but Thunderwolf Cavalry have no place in the game, at least at launching point...... Maybe like a vehicle or as something given to the best in the chapter and very very limited in number. They could add it in the beta to test it out how it will effect the game for like a week or so, just so that we could see what the impact would be.
Undesmountable cavalry? Bad idea in terms of gameplay, specially when people will mounting and dismounting vehicles. Not only will it be inmersion braking seeing people running out of rhinos while you can't hop off a godamn wolf, but if we assume some areas will be restricted to infantry, undesmountable infantry will be severely limiting. Im sorry, if the devs keep going on the TPS PS2-like combat direction they imply to be taken, cavalry isn't feasable.
It depends how the devs really will implement vehicles. If they want all space marines to hop in and out/on vehicles like PS2, then no. Thunderwolf Cavalry won't work in any practical manner. But this is what I wished would happen: If you CHOSE to buy and drive a rhino, then THAT is the role you chose. You shouldn't be allowed to leave it (or you can only leave it once it gets destroyed). Oh you can't leave and run in with your allies, who are dedicated infantry, to cap a building? Too bad. You chose to be a transport runner for that life. That's what you should be. For example, I don't want to see dozens of freakin unmanned/abandoned bikes and fast moving vehicles outside a building complex or base as a means to simply get somewhere then ditch. And I do understand that in order to translate a game from one medium to another (tabletop to pc), mechanics need to change, and I'm okay with that. But since the devs said they are doing their best to stay true to the tabletop, then you have to consider that tanks, bikes, thunderwolves, etc., DON'T have a mechanic for a marine driver/operator to dismount and suddenly become another infantryman. It's a whole separate unit that lives/dies with it's vehicle/mount. There should at LEAST be some incentive for players to stick with their vehicle and rarely ever leave it.