A couple of advantages to WiFi would be, rather than move the AP, you could simply put a repeater(wifi amp) in the basement should signal from the above floors become an issue.
Moving the AP simply to reduce your run of cat6 wouldn't be necessary, thus keeping your great coverage!
I run a dedicated router for VPN over WiFi no problem!
I agree with you that VOIP over wifi is currently only 'half duplex' which presents an issue of a direct conflict with Voice conversations which tend to be bi-directional.
Ethernet is 'full duplex' which relieves this problem somewhat, however issues can still exist.
VOIP over wifi can be resource hogging on the network, however this issue can be resolved today by using an AP that supports the 5ghz band allowing you to move 'high bandwidth' devices to this spectrum. Not only is the 5GHz band less cluttered, it also has many more channels to use for overlapping coverage, this ofcourse, differs from country to country but here in Australia we have 21 non-overlapping 20MHz channels (or 10 for channel-bonded 802.11n).
This allows us to reserve a dedicated channel just for VOIP which can also be done on the 2.4ghz band to improve performance by giving voip more bandwidth.
In my opinion, 5ghz would be the way to go as this would give you supreme data throughput and allow multiple AP's without restriction.
Its something to consider anyway!
Another disadvantage is that most voip wifi handsets only support very basic wifi encryption (namely WEP) so it is important to either use a unit that supports WPA2, or isolate your "Voice" network from everything else using appropriate security policies on your APs, and routers/firewalls etc which is not hard to do!
Naturally, protecting your 'voice' traffic over Ethernet is not necessary.
Edited by Replicator, 25 July 2018 - 09:59 PM.