I've been running with ssh-rsa disabled for a while (with a config based on https://infosec.mozilla.org/guidelines/openssh#modern-openss... ) and it's been pretty smooth. Support for better algorithms is widespread, with a few exceptions (like bazaar.launchpad.net).
One gotcha: OpenWrt does not enable ECDSA by default[1] and only recently enabled support for ed25519 by default.[2][3] It's available in release candidates for 21.02, but not in current stable releases. So if you're running a stable release you'll need to either add `PubkeyAcceptedKeyTypes +ssh-rsa` to your client ssh_config or use a custom build of OpenWrt with DROPBEAR_ECC or DROPBEAR_ECC_FULL enabled.
One gotcha: OpenWrt does not enable ECDSA by default[1] and only recently enabled support for ed25519 by default.[2][3] It's available in release candidates for 21.02, but not in current stable releases. So if you're running a stable release you'll need to either add `PubkeyAcceptedKeyTypes +ssh-rsa` to your client ssh_config or use a custom build of OpenWrt with DROPBEAR_ECC or DROPBEAR_ECC_FULL enabled.
[1]: https://bugs.openwrt.org/index.php?do=details&task_id=786
[2]: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=d0...
[3]: https://bugs.openwrt.org/index.php?do=details&task_id=3216&s...
[4]: https://bugs.openwrt.org/index.php?do=details&task_id=3452