Yeah agreed it is the multi-team regions that stink, particularly if the RSN they are protecting isn't really even available in some of those outlier regions. I think if you live in Hartford and are actually able to purchase the RSNs for both Boston and NY, no problem. If not, there should be a way to figure out (if not MLB.TV than the ability to buy a local streaming package w/o having the cable subscription).
I travel a lot too but I can't really expect MLB to worry about that narrow a niche. I do remember one time I was in LA and the Phillies were playing the Dodgers and I couldn't get the Dodgers' station. But I can't remember the last time I was in a Philly hotel or the Lehigh Valley where I couldn't get NBC Sports Philly or any other channel the game was on. The only exception was a family member with a satellite dish, since that carriage agreeement still never happened, even after the old PRISM loophole finally got overturned.
At this point I'm happy to just find other ways to watch when a roadblock does go up (pirate streams, VPN, changing my location). In your scenario, a family member's cable log-in would get you the ability to stream NBC Sports Philly while in Philly, if you have that option.
Would be nice if MLB.TV had single game purchases like the NBA too.