First of all, we don't really know enough about Halo 5's modes to say how they could best be organized in matchmaking yet. It is already clear that the game is being splintered into various parts with the Arena component (which contains Breakout with completely different core settings) and the scary, unknown new take on Big Team Battle. We aren't even sure if ranks will (or should) apply beyond the Arena at all, we just don't have enough information yet. This splintering is going to make a mess even without considering the possibility of the addition of Legacy Halo settings in matchmaking. Unfortunately, including Legacy settings in matchmaking would not be as simple as making a playlist with sprint and clamber disabled on dev maps anyway. The lateral scaling for maps designed for sprint is vastly different from traditional Halo maps, and the same can be said for the vertical scaling when clamber enters the equation. In other words, you do not want to play Legacy settings on Truth because it is overscaled and would play terribly. A legacy playlist containing forge maps would be possible in the future, but I am not hopeful for it to have the best settings or maps.
At this point, Halo players need to accept that we are being marginalized. We'll have our Legacy settings to play in custom games, and those settings should be pretty good all things considered. We'll have our fun. It just won't be in matchmaking. All of the splintering is a shame, but that began during Reach. It isn't going anywhere.
Also, your model includes three distinct sections in matchmaking, each with their own group of playlists. Unless Halo 5's population is significantly greater than that of Halo 4's or MCC's, it will not be able to sustain this many playlists. Most would be populated by only a handful of players at any given time. This model also presents a curation issue in that it includes three simultaneous rotating playlists. This would create an extensive amount of testing work for the sustain team.
