While I find it difficult to guess what the Spurs might do and if there are any offseason moves still to be made, as thing currently stand I think a good case can be made for putting Manu back in to the starting lineup.
There are currently four wings that should see the majority of the minutes at the "SG" and "SF" spots: Kawhi, Danny, Manu and Marco. Kawhi and Danny are the better defenders, Manu and Marco the better ballhandlers. Much like the Spurs this past season tried to keep either Tim or Tiago on the court at all times to avoid a Bonner/Diaw pairing, I think they'd want to keep either Kawhi or Danny on the floor at all times and avoid having Manu and Marco as the two wings (with a possible exception of when Kawhi is playing small ball PF).
Having either Kawhi on the floor at all times doesn't mean that they can't spend a fair amount of time on the court together. During the playoffs they spent about 25 mpg on the floor together, with Kawhi spending an additional 12 mpg without Danny and Danny spending 8 mpg without Kawhi. They were both playing longer minutes in the playoffs, so their regular season mpg together is likely to be more like 18 mpg with each playing some 14 mpg without the other. If the Spurs are to play any small ball minutes, they likely should do so within the time that both Danny and Kawhi are on the floor. That likely would not be at the start of halves but at some other point in the game.
Starting Manu with Kawhi could be a good use of the time that Kawhi will be on the floor without Danny. Whatever shortcomings Manu might have on defense will be helped out by the fact that not only will Kawhi be out there with him, but both Tim and Tiago. When Danny enters the half for Manu would be about the time that Boris comes in for either Tim or Tiago. Danny's better defense but lesser playmaking balances out with Boris' lesser defense but better playmaking. At a later point Marco goes in for Kawhi with Danny sliding over to the SF position.
One reason often given for having Manu come off the bench was so that his playmaking would be in the game at a point when Tony might rest since Gary Neal was not much of a playmaker in place of Tony. While either Nando or Cory will hopefully have improved with experience while relieving Tony, they now have the assist of having Marco and/or Boris in the game with them for playmaking. Tony and Manu in the game together will give each the opportunity to play off the ball more often. Danny might actually play more minutes off the bench, but be in the game with various other players able to run the offense.
The last season that Manu was consistently a starter, 2010-11, he was able to play 80 games before suffering a freak injury at the end of the regular season which caused him to miss the first playoff game. While I'd not expect him to attempt to start every game and sit out a few on back-to-backs, this season most of those back-to-backs have a fair amount of rest around them so that he might play as many as 70. Last season coming off the bench and he seemed to suffer a number of muscle tweaks. It might be advantageous if he gets more of his minutes at the start of halves rather than entering the game after sitting for a number of minutes.
I would figure both Kawhi and Danny putting in close to 32 mpg with an 18-20 minute overlap, That 64 minute total would likely include an average of 4 where Kawhi is playing the "PF". Manu might average around 20 mpg and Marco 16 for a total of 96 minutes for the two wings.