When R&D is implamented will all factions and characters be able to use it?
Can someone add a Medical Room to a Lamdba Shuttle or a Hanger Bay to a Sabaoth Destroyer? With R&D will you be able to Create entities ( and Datacards) and use them like the ones currently in the game?

Whether or not you will be able to modify rooms or add certain individual features (e.g. docking bay) hasn't been decided yet.

Once R&D is released, you will be able to research and develop new entities and create new datacards.

Will everyone be aloud to use R&D or will it be like Mining, Production and Recycling?

Your best bet will be to wait for R&D to be implemented to know the answer to that question, as any possible answers are educated guesses at best and may yet still be wrong.

As Ceso said, pretty much anything regarding upcoming features can change before its introduced. We know it will be a tech tree. Pretty much beyond that its anyones guess.

However, as a guess, datacards are only owned by factions at the moment. R&D creates new datacards. Putting those together would imply that it would be restricted to factions. However personal inventories have a DC section, so it maybe that players can own DCs personally, which could mean no, factions are no needed.