AFAIK, no team has ever used a set rotation of 6 starters for an extended period. First, you want your best starter(s) to start every fifth game, maybe even moving other starters back when there's a day off in order to start them every fifth day. Second, even though it would seem that a fifth day off between starts would enable a starter to perform better, it's my understanding that this is often not the case. Of course, spot starts will be needed in certain circumstances such as doubleheaders or for someone to skip a start but IMHO a 6-man rotation is a non-starter (pardon the play on words).
The issue at hand then becomes choosing which five pitchers to put in the rotation. Right now both Ober and Varland appear more ready and able to perform in the majors than Maeda, both appear to have higher ceilings than Maeda, and both are much more likely to be part of the future than Maeda. Also, Maeda should not automatically be entitled to a spot in the rotation. Coming off TJ he's an unknown quantity and he's 35 years old. It makes sense to give him opportunities to demonstrate what he can do but I think those opportunities would be best given in a relief role. Use him when a pitching change is indicated in the 5th or 6th inning, let him go 3 innings or so, and if things go better for him than for someone in the rotation consider making a change.