I fell into this trap with our app. We have an iot app that controls 3 generations of hardware now. The first generation device is only visible via Netbios lookup, which runs afoul of this new multicast lockdown. The later 2 generations support Bonjour (mdns) lookup. Unfortunately we are still running into problems with customer routers that block or interfere with Bonjour service discovery, so we still fall back on Netbios even in current generation hardware. Luckily we have history with Apple so the approval was fairly straightforward, but I can't imagine what the process would entail for a new company/new product.
We "fixed" it with broadcast, it was the only way.
There are indeed a number of old routers out there that do not work with mDNS well. This is still a problem, but most <5yo routers seem to handle it okay (with the caveat that there are a number of cheap APs and extenders that are completely broken at basic TCP/IP when clients switch).
We use broadcast for device-to-device discovery, vs device-to-phone. It makes for noisy networks, but works better than mDNS on a wide range of hardware.
