Pretty hard. We've only had 3 or 4 total, I think. arm11 is much easier. That's why we have still have homebrew/userland on 11.3. I read 11.3 made it easier for arm11 exploit. Someone may have an arm9 exploit they haven't released, but I wouldn't get my hopes up. Your best bet is to sell your 11.3 and get 11.2 or less. Next time ask the what the firmware is.*sigh* Well shit. I guess there goes my plan for hacking my n3ds. I should've created a nand dump of my o3ds or something.
Side note: How hard would it be to make an a9lh hack on 11.3?