I absolutely have to disagree on rifle grenades here. I have never heard them mentioned before in WWI, and while they could have certainly existed, this in my eye means they either weren't common, or were not all that good.
Furthermore, rifle nades are just exploited so horribly in game. At the very least I hope they are fuse, and not impact, based. Impact based just turns them into long range accurate artillery from the hip, from everything I've seen. Even fuses would probably not alleviate that. One of the main uses in RO atm is they are one of the few weapons where one can take out an enemy without sacrificing mobility for a limited time (every other weapon except melee you cannot sprint and fire, and often you have to find cover/place to rest your weapon, go into IS, and kill the person.) The main disadvantage of this is that 1) Grenade ranges are not all that long, 2) to get an accurate grenade throw one has to often be sprinting in a straight line for a second or two, and 3) having grenades out are risky, if somebody appears suddenly you are often screwed, and with the german nades you have to also watch the fuse.
None of these disadvantages are in rifle nades, they have longer range, and I'm guessing they will be fairly accurate.
If they are to be in game, at the very least, limit it to one person, in a specialist role similiar to sniper or MGer.