Note that I don't own a multi-filament setup so I can't speak from personal experience, but this is after I'd done extensive research into it and determined it wasn't worth it for my personal use case.

What kind of parts will you be printing in multi-material? The kind of prints you are doing will greatly determine the best approach. Some smaller prints with many filament changes will result in purge blocks with more mass than the part itself.. ie more than double normal filament usage.

IMO the tool changers are the way to go and I think we will be seeing more of them in higher end machines. I personally wouldn't use multiple materials for the sake of colors, but different tool heads offers the ability to print with different materials at different temperatures, as well as different nozzle sizes or different setups altogether. For example you can have a 0.6 volcano nozzle for the bulk of your print, a standard 0.2 nozzle with the same filament for fine details, and a 0.4 nozzle with a water soluble filament for supports.

This is just speculation, but I'm betting that we'll see tool changers with more than just extruders on deck - imagine if you could add a Dremel head for post-print sanding, or a drill bit to clear out holes.