With the recent announcement of Recon Intel, it is now possible to get a unit with scout 4.

So far, if a unit with scout gets an additional scout keyword via the new mission from the Priority Supplies Battlefield Expansion, their scout volume would increase by 1.

For example Rebel Commandos have Scout 2. If you choose this mission where all units get Scout 1 at the beginning of the first round, the commandos get Scout 3 instead and you use the 3 speed template to perform their scout move.

But how do you manage it if these Rebel Commandos are equipped with Recon Intel? Scout 4 means twice the speed 2 template or once speed 3 and once speed1? or is it your choice?

Or is there a hardcap of 3 on keywords?

Page 46 of the rules reference guide says that Scout X can only get up to a value of 3, which makes sense given that there's no speed 4 movement tool. You should check the Rules Reference for this type of question, it's pretty good at being cut and dry about this type of stuff. FFG is doing a decent job keeping the rules for this game pretty straight.