Just another angle on this. Did a clean install of Yosemite through v10.10.2 - obviously no Photos is available in that version.
Installed iLife with iPhoto that ran on Mavericks (iPhoto 9.4.3). This version of iPhoto won't run on Yosemite and going to the App store there are no updates available.
So it appears, if you upgrade to Yosemite you will not be able to access iPhoto, unless you previously "purchased" (for free) the somewhat crippled iPhoto 9.5 (9.6, 9.6.1)...it'll be either v1.0 Photos in OS X v10.10.3 or stick with the older iPhoto in Mavericks/Mountain Lion. This is something that appears to have fell through the cracks and Apple should offer this update for folks that still want it.
Installed iLife with iPhoto that ran on Mavericks (iPhoto 9.4.3). This version of iPhoto won't run on Yosemite and going to the App store there are no updates available.
So it appears, if you upgrade to Yosemite you will not be able to access iPhoto, unless you previously "purchased" (for free) the somewhat crippled iPhoto 9.5 (9.6, 9.6.1)...it'll be either v1.0 Photos in OS X v10.10.3 or stick with the older iPhoto in Mavericks/Mountain Lion. This is something that appears to have fell through the cracks and Apple should offer this update for folks that still want it.