I have to agree regarding the droids appearing in ROGUE ONE. It was certainly plausible given the timeline and mission, but it did come across as if they were shoehorned into the film. I think it probably could have been handled a bit more organically in a direct interaction with Bail Organa.
If it does happen in SOLO? I think that it may link back to a line from ANH where Threepio says...
"We'll be sent to the spice mines of Kessel and smashed into who knows what". And from some of the toy releases, it seems like there may be some sort of fighting/working droids on Kessel, which figures into the movie in some way.