I'm not sure they will even be able to do 5e TB exactly. My understanding ( not a PnP player since 2e ) is that you can have 1 reaction per turn, but there could be many opportunities to take that one reaction. So the game would effectively need to offer each player a reaction every time one became possible, until the reaction is taken. That would make an already slow combat experience even slower.
I believe that reactions will be automatic. Probably something like a menu players can open on their turn which will let them select which reaction (or reactions) they'll look for, and what the trigger will be. If the trigger is met, the reaction will be used automatically.