According to "the interweb" oxygen permeation through the casing of a tire damages the casing (I can believe this). It is less clear if water can cause similar damage (rusty steel belts?). However, the rate of damage and permeation is very low and it is primarily a concern on heavy-duty truck tires that are expected to last 100,000 miles per retread AND be usable after several retreads. Plus large on-roadtrucks runs 100+ PSI tire pressures.
Permeation of air through bicycle tires is a bigger problem. The rubber is thinner (about 1mm), the pressure is greater (I run 130PSI), and the ratio of air volume to tire surface area is smaller compared to a car tire. I have to pump up the tires weekly (10-15psi drop per week). Interestingly, I find that the first one or two bicycle tire fill ups leak down noticeably more than subsequent fill ups, perhaps because it is predominantly oxygen that is leaking out from the initial fill up?
If I read the data on the web properly, Argon should perform even better than N2. Argon atoms appear to be several times larger than N2 molecules. Dry air is 78% N2, 21% O2 and 1% Ar (round numbers). You can buy Ar at your local welding shop, just like N2. Although Argon exhibits ideal gas behavior just like N2 and O2, its dynamic behavior is different because it is mono-atomic. I do not know if that would be different better, worse or not-so's-you'ld-notice.
Filling a tubeless tire with a selected gas is not easy, as the cavity cannot be evacuated.