The Nexus 5 is so good I wouldn't hesitate to buy it...even in July. Its not like you are in a contract. If I needed a phone I would still choose it. If and when the N6 comes out I would probably get that as well and either use the N5 as a spare or sell it.
This is just me but there isn't anything the N5 doesn't have that I even care about. Its a great phone. With great instantly upgradable software. If Google keeps puting out phones this good I'll continue to support them as much as I can. I hate to think of the day when I have to go back to the compromises of a carrier phone.
I'm sure I am alone in my opinion...but I am not sure the N6 will even be as good as the N5! They might decide to go back to 16GB for all we know. Or do some other cost saving measure. Including not making it at all, which may leave us with the N5 as the last great pure G phone. Its the only phone I still get excited about.