A direct boot into a game, idk. But scene the homebrew launcher can load games then I would think it should be possible to do a load a bare bones HBL(for speed/stability) then do a direct load of a game, but there are a few issues with this:
1: It would have all of the same issues that the HBL has like no access to the extradat/dlc/update that a game might have like loading a game on a different unlinked NAND or a different system. Also, you won't have access to your friends list, so doing it this way would mean that you have any friends.
2: I don't know how a9lh treats the HBL s I haven't taken the time to switch yet, but to load a CIA it would have to be set to the right NAND when it loads. But that shouldn't be to much of a problem though (the 3ds already have an option to load a game card on boot but I forget the button combination, and I think it doesn't work for out of region games).
3. No home menu to load into, so a game would crash unless something else is set to the home menu button like the screen shot feature HANS has.
4. It would take the time it would take to load haveHBL and then the game with a chance of the launcher crashing too.
5. The region free laufixed can only do game cards, but HANS won't work with all games, so a different way of loading a game would be needed.
So once everything is set up, and the SD game data and load time is fixed, it would be possible to do a indirect loading of game on boot, and could maybe load a HANS hack and/or NTR this way too.