It is possible to set up a formal special interest group on LinkedIn, and perhaps someone will volunteer to set one up for FlyerTalk members. Many such groups already exist on LinkedIn (college alumni groups, former employees of various companies, other types of organizations).

However, I think a lot of people are reluctant to list FlyerTalk as an interest (or they list it cryptically), because 1) They might not want to send prospective employers over to this board to see how nutty FTers are and/or 2) being a "frequent traveler" might look bad (i.e., an indication that one takes a lot of vacations).

Of course, one could also put a positive spin on FT membership, at least for employers where there is frequent business travel!