Sounds like Dash would be a good option. I suspect the community would be open to it’s use in this manner as the Bitcoin Cash community is. Dash has a shorter block time and instantly secured transactions. Since nodes on Dash are paid the economic viability of scaling them is known. I run a masternode myself and have done the math on scaling it up based on my current resource usage and the current costs of available cloud hosting services. Even if the price of Dash didn’t rise and hosting costs didn’t drop the network would be sustainable for doubling transaction volume 9-10 times (6 million tx a day or so). We also know that the blocksize for Dash will be increased if the fees grow to be more than 1 US cent since the masternodes were polled and voted overwhelmingly in support of that.
Edit: That was calculated assuming 1 cent per tx fee on average. I also assumed it would take until 2028 to get to that level and fees would make up a substantial portion of income for nodes at that point.