After SBSP hit 5.2M on a Monday holiday in November, I think 4.0M is doable. Plus, the SBSP special and the BW premiere has been promoted since December and once the SaC special is done next Saturday, I'd expect everything will shift over to animation with the emphasis being SBSP/BW on 17th. This gives almost a month worth of promotion. If Nick plays it's card right, I could see BW out performing SJC's premiere numbers. And with SJC, TMNT, and RI all having premieres in February as well, (KFP, PoM, MvA to a lesser extent), this could really be a defining month for the animation.
SJC was the turning point for Nick. They were obviously headed in the CGI and Dreamworks route, realized it was one-dimensional when the ratings plummeted, and the SJC success righted the ship. SJC, BW, and I'd assume BS and PGBC are all throwbacks to 90s Nick. People can say it's ripping off CN's RS and AT, but really it's Nick just going back to it's roots. Nick will clearly be THE No. 1 network again in animation for the foreseeable future. I'd say Nick has really distanced themselves from CN and DC in that department. My heart has softened to BW the more promos I've seen. I think it can definitely be a hit like SJC.