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.
But in such an event, there would still be a president-elect, so the line of succession would not be invoked.
Oh I see what you mean now. But what would happen in a situation where the pres/vp haven't sworn in for a few days?
Regardless, I like PiT's idea. Having a line of succession is good, but if someone is going to be president for a long period of time, I think it would be best if that person actually wants to be president.