Or beef up security so not just anyone can board it, or be more mindful of where/how you park it... ship interiors aren't just for the cmdr
Or switch to the Horizons client for docking at stations so people can't board it, or do a quick relog after takeoff to drop them out.
There's lots of ways to do ship interiors, certainly; boarding and repairs are commonly suggested features but not one which I think works very well in the context of player ships with the rest of the game. As you say, it would require much wider impacts on how the rest of the game operates ... and those impacts wouldn't be themselves universally popular.
1) It's a rare ship which actually takes significant module damage in combat, for an experienced player - super-engineered shields will tend to stop most NPCs ever doing module damage, and a dedicated combat ship is likely to have some MRPs too, and maybe an AFMU to keep the MRPs topped up on certain builds. Repair and resupply is often just a couple of minutes supercruise away, and most modules have all-or-nothing functionality where 1% integrity is as good as 100% for most performance factors. So for in-combat repairs to become important, shield-penetrating module damage would need to become a routine capability of most weapon classes, and even minor module damage would need to lead to noticeable performance loss. That's a really major change to a lot of things, which means in most cases the interior implementation would just be getting ships
back to the combat capability they currently have.
2) The current model is that if your ship is docked at a station, it's safe (Odyssey ground ports aside). Changing that to mean that, if anything, it's in
more danger than it would be just floating in space next to the station is a major difference to how the game works. In terms of PvP boarding (the least likely sort), there'd also need to be some way to guarantee a ship stayed docked long enough to get to it - at the moment, if you're not looking at the mission board, you can dock, sell cargo, buy next cargo, and be launching again in much less than a minute (you rarely have to even descend into the hangar where the elevators are in the first place) - obviously, NPC boarders could just be deemed to have got aboard.
I would expect the focus of a "ship interiors" expansion to be essentially cosmetic
if looking at the player's own ship: that interior exists because it may as well having modelled it for the NPC ships. Boarding NPC ships for salvage, repairs, sabotage, etc. could be included without having to rewrite the existing game mechanics too much, and without providing an encouragement to log into Horizons even if you have Odyssey, and would provide a wider variety of environments for on-foot activities ... whether, of course, that wider environment is worth the implementation, given that you can already do all those things on foot at Odyssey surface settlements and it's hardly been a feature which has become the "must do" thing, is probably why Frontier have said it's not on their list right now.