Hi there. It seems this idea is sort of new to you - and if not then others might not understand, so let me quickly explain. For either a backup or primary link, depending on which is best, one will run either a TINC (by far the easiest, https://gitlab.ctwug.za.net/ctwug/tinc_configs - I would recommend googling the system).
In the case of some setups you would run a tunnel (VPN) through the internet and provide WUG traffic through there to your destination. Eg: Might Highsite > My home internet > Central Server (TN) > Next hop. This would be using my own internet connection to tunnel WUG traffic to another internet connection, and in now way provide the WUG with internet - it's wug over internet, not internet over wug .
The part where you mention if the proxy will handle a large amount of the user's data, that varies a lot. If you have a highsite and a 100mbit/s fibre link and on the other side about 8+ hops away is another guy who also has a highsite and a 100mbit/s link - or similar, it makes sense since unless the network is running 802.11ac with absolute best possible everything, you might only then have >100mbit/s and have a better link than the tunnel.
You generally have your traffic going through the shortest path possible - which might not always be the best path, however you can use routing filters to adjust this to have the better link take preference, and the link that is not performing so well will only kick in if the other link goes down. Depending on how you set your filters up, you will of course want to still provide that link you're filtering out with a link at least - it's users need some form of a wireless link unless there are multiple other backbones.
Currently I am running only more than 6 hops will go through my tunnel (and of course all JAWUG and CTWUG traffic), since I believe the wireless link should be preferred - we're still a Wireless User Group. Further it gets used if there is no other possible path, since we have only got two links between our "north" and "south" parts, and the reliability of one of them is not so well, if it goes down and the other is too far (too many hops), mine provides the North with a backup link to the South (I'm in the South).
The TINC setup at my house was actually set up by @spin who helped a lot, and the TN (dedicated mikrotik at a datacenter) link which links parts of PTAWUG together and then JA/CT/PTA use this also, above TINC. @spin and @silver helped set the latest parts up, however the original idea was brought by @RaynoP who is no longer running his link due to the cost of bandwidth and the lack of appreciation he was given.
The "test run" you're referring to has already existed for quite a while . It is definitely up to the CTWUG Committee to decide if certain IP's get their routes changed globally throughout the WUG, and it is their job to implement it.
Referring to the part where you mentioned a World Wide Wug, have a look at a German network called Freifunk, they're basically the German WUG, and are a huge network with extremely well set up tech. It would be nice to link with them one day, although I see dozens of IP clashes already and that will probably have to be sorted out. For South Africa, it is good that our WUG's communicate with each other and link with each other (excluding SOWUG, not saying more about them..).
Thank you for the compliments also, however I would like to point out that I barely did any of the work mentioned regarding the inter-wug setup and so on, I just did the gaming part, and that I was also receiving help from the PTAWUG admins at the time.