There are a lot of teams that still run a 3-4 as a base defense. I believe a majority of the SEC along with some PAC schools run a 3-4 as a base. I could see the advantages of running one but there are also disadvantages. You can get more speed on the field but you will also lose size. It is a pick your poison kind of deal.
Who runs it in those conferences? Alabama? Georgia may have. It's not coming. The NT and OLB positions are very difficult to recruit effectively for.
Alabama, Georgia, Kentucky, A&M, Tennessee and Florida have ran a 3-4 as their base in the last year or 2. Both Mississippi schools and LSU are looking to run a 3-4 this coming year. Notre Dame has ran a 3-4 since Kelly took over. In the Pac, Stanford, Oregon and Washington run a 3-4 along with Cal. Indiana, Maryland and Wisconsin have been running a 3-4 off and on.
As far as recruiting goes, it isn't any different then recruiting for a 4-3. You have one less DT/NG to recruit and you recruit smaller DEs that can also play OLB. We have recruited some damn good OLB recruits the last couple years. The only thing hurting is the DT/NG recruiting.
The one big difference is having a legit NT. Would have worked pretty well last year with Valentine at the NT with Collins and McMullen as the DEs. Not sure we really have a legit NT right now. Other than that, it would probably help cover for also not having a legit edge rusher at DE.