We're definitely considering it. We introduced the limits a while back as an experiment. In most cases, I believe the current limits don't make a lot of sense. Fundamentally, we were hoping to encourage the deployment of Tailscale to end devices (partially to increase users' security, partially to get a better idea of how widely Tailscale is actually being used). Unfortunately, the limits introduce the kinds of headaches that you're describing (and for IoT it can be a showstopper). The net effect across all users could be to actually discourage people from having fun and tinkering with Tailscale, which is the last thing we want.
Would you mind describing some of the other use cases you have for subnet routers? Do you have other mini k8s clusters you want to use them for? Other things? I'd love to learn more.