Would it be too hard to add non TCP traffic tunneling? This already supports DNS traffic through the tunnel but I wonder it is feasible to tunnel all kinds of traffic (UDP and ICMP mostly) through it?
The SSH connection is inherently a reliable stream, so you need to be careful - it should work if you drop UDP packets if the ssh stream's send buffer is full, but there might be severe performance traps down that route. Maybe an expert can elaborate. The other issue is you'd need to do manual NAT-like connection tracking to match up sources and destinations. I could imagine many UDP-based protocols not taking kindly to that sort of treatment.
By the way, (open-)ssh itself supports a tun/tap VPN mode (-w I believe) that creates actual network interfaces on the two endpoints, and thus can transport any IP traffic. It needs to be explicitly enabled on the server, and needs kernel tun/tap support, which is usually missing on VPSes that don't let you run your own kernel (modules).
By the way, (open-)ssh itself supports a tun/tap VPN mode (-w I believe) that creates actual network interfaces on the two endpoints, and thus can transport any IP traffic. It needs to be explicitly enabled on the server, and needs kernel tun/tap support, which is usually missing on VPSes that don't let you run your own kernel (modules).