It seems like it could be abused to force the Speaker to resign.
I don't really understand what you mean by this. Are you suggesting that the SoFE would purposefully hold up the certification of the election to force the Speaker out of office? I don't see what anyone would gain from such an obvious abuse of power, especially considering vacancies in the House of Representatives are filled by appointment of the former representative's party. All things considered, I think the potential for abuse of power is much greater in a scenario where a single officer is both president and Speaker of the House.
What I mean is that it sounds like the President and Vice President could be awol (or refuse to swear in at the "appointed hour") which would force the interim president to take office. Then the president swears in later and the interim president is out of luck.
I would hope that nobody would be that nefarious (but we should also prepare for such), but regardless we should probably include a clause that the officers can decline the role of Interim President, lest we should encounter a scenario where the Speaker of the House is randomly ejected.