Photos will exceed the needs of 99% of Mac users.
Allow plug-ins for the remaining 1%.
I don't see the problem.
Then you are likely not an heavy Aperture user. Because it is a problem for Aperture users.
And please don't tell me that "you can keep using Aperture for as long as you want, it won't stop working on your Mac, you won't lose what's there already, etc...". It actually MAY and likely WILL stop working with a future release of OS X, possibly as soon as October (assuming Apple's recent OS X upgrade schedule). And with no continuing Apple development, minimally new cameras will lack RAW support, essentially making Aperture useless.
Aside from ceasing of Aperture development, photographers that use and RELY on Aperture simply don't know Apples plans! Maybe Photos becomes a full Aperture replacement...maybe. But when? 6 months when new plug-ins fill the gap? 2 years? Ever?
And don't kid yourself, people RELY on Aperture as the primary tool for their photography business and/or hobby. Primary tool, not some "app" that can simply be replaced. Moving from Aperture to Lightroom is as, or even more, significant that moving from a Mac to Windows.
Again, if you use iPhoto or some other program and will find value in Photos, that's awesome for you. If you use Aperture, the new Photos program and the eventual/likely/necessary move from Aperture is a real problem.