In terms of the pure linux routing solution, that is pretty interesting... Does it require that the remote machine has two physical interfaces or could you do the same with virtual interfaces like eth0:0 and eth0:1. Either way there are a few drawbacks with that solution. It will send 100% of your traffic through it rather than being able to selectively proxy. Also it only round robins so there is no intelligent load balancing as there is in tunnel splitter.
Ahh.. read the mighty and mysterious tome of lartc just a bit deeper and all will be revealed. The teql becomes an interface all its own and with the black arts of packet-mark-itsu, and route-fu all this and much more can be accomplished.
I actually tried to write a packet reordering buffer but one of my connections had a pretty big latency so added together, my rtt became huge. My solution was actually to use windows less, and route small interactive stuff like DNS on the low latency, but slow connection.
Oh and virtual interfaces and vlans will both do just fine. I only ever had one nic in my main box, my direcway modem and dialup-box were hooked to it via a little switch.
Yes, I load-balanced a satellite link and a phone modem.