Do the QoS rules also apply to traffic destined to a Client VPN (Windows laptops etc)
So say i, "suddenly" have 200 client VPNs connecting in, can I create QoS rules / whatever to differentiate traffic from different internal hosts going outbound and if so, what limitation / caveats/gotchas am i likely encounter?
Which do you want first, the bad news or the bad news?
You can't prioritize traffic over the general internet and certainly not from home offices with residential internet.
The whole internet is being stressed right now and I would try to find other solutions besides VPN wherever possible. For example, file sharing through Dropbox or similar and screen share with VNC, etc.
Client VPN is just going to work a little worse than any other type of connection because of the encryption overhead and resources it takes on the firewall and client machine.
As @BrandonS says, if you have 'fat client' devices like Windows or Mac PCs using local applications and clients connecting to central servers and applications, it's going to be quite bad with people working from home.
Cloud services, OneDrive syncing local files to central server for example, however this only moves the problem as has been seen today
Set up the VPN and use a system such as riverbed that has a compression agent on the client PC and a server in the Datacenter
VPN with Citrix XenApp in Datacenter, works over mobile connections and basic broadband
VPN with VDI in Datacenter, more performant than Citrix XenApp but bigger overhead.