Probably harder to implement to be honest, considering the biker squads are limited (as far as I know) to 2 squad members. One driver, one gunner. I’m still yet to uprade either of my biker squads because of the incredibly excessive XP requirements.
To me though, it just proves that biker squad XP gain is a little unbalanced compared to APCs or Trucks. I hope the devs take another look at that at some point.
I don’t think it’s problematic. It would work just like with tank squads.
For example squad which can use grant can use up to 6 people.
But if you use different vehicle. For example crusader. 3 cremans and 3 other would be grey out.
So if you pick bike, you will be able to use only 2 guys. With jeeps and similar vehicles, you could use more that 2.
And tbh, I think they should 3 men bikes squad as well to TTs.
Regardless, before they add more bikes, they should finally do something about the terrain.
The best thing would probably be a complete removal of the collision model for small objects etc.
And especially for the railways, I even completely got stuck with APC on those yesterday.
Until then, it’s probably a bit pointless to think about adding similar vehicles, that would suffer constantly due to getting stuck on a rock or something anyway.
Riding a motorcycle is like a circus, except with bumps and riding upside down. Recently, on the sdkfz hangar map, I couldn’t cross the railway tracks, the vehicle kept hanging up. I had to go to the edge of the map to pass.
DEV’s not going to consider offering a squad like this unless their is some coin in it for them. And if they did, they gonna want like 4,500 or 5,000 gold for it, over priced like usual.
And if they did, they gonna want like 4,500 or 5,000 gold for it, over priced like usual. 
