@stsp A better long term solution is adding the ability of the driver to pick up a new device from a "quirk file". Of course keep the original hard coded list but add the ability to add new devices on the fly.
@stsp Entireley in agreement in the longer term. However, such a mechanism can rescue an install until the next release which includes the device is available.
@Dianora One problem with your suggested approach is that it encourages local config changes which may end up not being shared. Whereas everyone benefits long term from modifications to the default device list in the kernel.
#OpenBSD tends to prefer out-of-the-box solutions over config files where possible. If no config file exists, users will be inclined to ask for better defaults instead of tweaking their config.