Surf already hits most electric immunes super effectively (A-Marowak and ground types). The entire point of running coverage is to get through things that your STABs will struggle with, and even though Psychic hits those electric immunes harder you're better using a little prediction to make some holes with your coverage.
You're right, Nasty Plot is a hard move to pull off against offense, but against stall where you'll actually need it it's pretty easy to pull off and makes Raichu entirely self-sustaining against a stall team - really breaking them up and making them much more manageable. Most of the time you won't actually need it, but I don't see an additional coverage move (TBolt, Psyshock and Surf covers a lot of bases) as hugely important anyway so why not run NP? I mean running extra coverage move isn't a bad idea, but I don't think Nasty Plot is a bad idea to get through stall either. They both serve different roles depending on what you want on the team, the former a better cleaning and the latter a better wall-breaker.
For the "on a timer" thing, Raichu is pretty fast so I don't think it's much of an issue. As I've mentioned, Nasty Plot isn't what you'll be wanting to use against offence anyway, there you will just rely on the superior speed and hard hits to get what you want to do done.
I think it's a bit short-sighted to rule it out as a valid set.