I think boarding should be treated like interdiction. Ie, a fast paced battle of skill and dexterity between target and assailant. I can imagine a scenario where you first need to disable the target ship, maybe involving a new weapon/module used to hold the ship in place for a short period of time while incurring a massive power draw to your own ship, adding a timed element to proceedings. Then there'd be a race against the clock to either a) repair damage and prepare countermeasures, or b) space walk to the target ship, find a randomly generated access port, and then actually breach the defences with some kind of brute force hack. I can even see a literal equivalent to the interdiction mini-game with the two pilots battling to lock/unlock entrance to the target ship, with group boardings having an automatic advantage (due to a greater ability to encircle the ship and locate the access port), while one-on-one manoeuvres being naturally weighted toward the target. If the target wins the game then they get to escape, leaving their assailant waiting for their power to come back on line, and also petty much unencumbered access to destroy their attacker(s). If the attacker wins then they get to take all cargo/materials/data from their target, making boarding an incredibly lucrative but highly risky endeavour. Stealing ships would not be an option because that's just not how the game works.