In theory, yes, in practice this will currently result in deliverability issues, both for servers which don't speak dmarc and for spam signals. I have tried thi

In theory, yes, in practice this will currently result in deliverability issues, both for servers which don't speak dmarc and for spam signals. I have tried this :) If this mode of operation was an explicit choice, this would give me the option to have a fallback SPF record for legacy mail systems, but most up-to-date servers will use the more secure and (for my use case) operationally simpler verification.