Eh, sounds like a bad idea to me. 1x1 is very different from group RP, just like the Arena is, so it's put in its own section to keep different things separate (because segregation on forums is actually a good thing for organization sake). Also, the whole of the 1x1 second on the old RPG was less active than Free or Casual, with ~1.3 million posts posts across all 1x1 boards where Free had ~2.2 million and Casual had ~2.6 million (numbers from the last archive.org snapshot of the old RPG front page).

Adding new interest check sections just for 1x1 would be unnecessary clutter that screws with the current intuitive setup (notice how there is no longer a general interest check forum, and how free int check is under free RP, casual under casual, 1x1 under 1x1, very intuitive organization), and Mahz has stated numerous times that he wants to implement a tagging system to make searching for things much easier. That'll surely come with tags for the RP level, so you'll be able to easily search for Advanced tagged threads in the 1x1 interest check section.

For now you can tag your threads with something like [Advanced] in front, maybe advocate to your fellow 1x1 folks that they should do the same to make things easier. Even that shouldn't be very necessary right now, seeing as there's few enough 1x1 Interest Checks that you should be able to scan through them all rather quickly.