Peplink works like magic - failing over very gracefully. The same can be achieved on Linux through network interface bonding, or on pfSense through Link Aggregation. You would need an intermediate server on the internet that supports the same. VPS servers are cheap and suitable for this purpose.
However, all this will not help reduce latency - which is what the original question is about.
For that, we need the solution proposed else where on this thread:
1. Client duplicates packets over two mobile links to an intermediate, user-controlled server.
2. This server sorts things out and discards the losing packet, and forwards the winner on to the real gaming server.