Kol Haover al divrei chachamim chayav misa

The gemara quotes a braisa which says that the Chachamim made a syag for Krias Shma that you should say it before midnight because otherwise you might go home, eat, drink and go to sleep and forget about shma. Therefore they said that you should go straight to shul after work and learn a little and then say Shma. The braisa concludes that anyone who transgresses the words of the Chachamim is chayav misa. I just wanted to mention a few points on this braisa.

1. When I first read the braisa, I understood that you're "chayav misa" if you don't say shma by midnight. Indeed that is how the Rabeinu Yona understood it because he asks why this is the only place in Shas that this language is used and he answers because here the Chachamim said that really you could say it all night but they said it's a syag to say it before midnight. They didn't want people to take it lightly and say "I won't forget so I'll say it later," so they gave it extra strength by adding the line that if you don't listen to them you're chayav misa. That's all very nice except that our gemara clearly doesn't learn like that. The Maadanei Yom Tov (under the Rosh) says that it's obvious that Rabeinu Yona didn't have the question that he asked in our gemara because our gemara asks the exact same question why it only says it here. Our gemara suggests two answers: either because of ones shina - the power of sleep is so strong that they felt that they had to emphasize the importance or to show that Maariv isn't a reshus but a chova. Obviously, the gemara is understanding the braisa very differntly than Rabeinu Yonah. The chachamim were saying you're chayav misa if you don't follow their entire routine. Not just on the takana to say Shma at the beginning of the night but even to go straight to shul and daven Maariv right after work.

2. The Pnei Yehoshua asks why do we need this special takana of the Chachamim to say shma right after work. We have that concept by every single mitzva called zerizin makdimin l'mitzvos? He answers that this is different because we have the limud zman shchiva so you might have thought that it's better to say shma as close to the time you go to sleep as possible. Therefore the chachamim said that despite that pasuk you should still say it as early as possible so you don't forget.

3. The gemara asks why we don't say so "Kol Haover al divrei chachamim chayav misa" anywhere else. I assume that the gemara means that it is true that you're chayav misa any time that you transgress something the Rabbis say but this is the only time that they bother to mention it when they taught the gezeira. Indeed, the mesoras hashas doesn't point to a single other place in all of Shas that uses this language. R' Akiva Eiger though points to gemara in Sota (also on 4b) that uses a slightly different term for someone who eats without washing netilas yadayim. It says that he is "neekar min haolam." Rashi explains that is because of our gemara that "kol haover ..." Why does the gemara (here it's an amora saying it and not a tanna but I think the question remains) feel the need to say that here as opposed to by all other mitzvos d'rabonon? Neither reason of the gemara applies. Furthermore it's exactly opposite the second answer because here netilas yadayim really is a reshus!

4. What kind of misa are we talking about here? Certainly not misa bidei adam. So it's misa bidei shamayim, right? But that doesn't really make sense either. Only specific mitzvos in the Torah is there misa bidei shamayim but most mitzvos don't even have that. So most mitzvos from the Torah don't have this punishment but mitzvos d'rabonnon do!?! I think that it must be that the Chachomim just say that there is a chiyuv misa but they can't possibly mean it literally. It's just used as a scare tactic. Rashi in sota though quotes a pasuk in Koheles to prove the concept "u'poretiz geder yishchenu nachash." I think then it does sound like a real misa bidei shamayim. If so then I really don't understand why Hashem would punish you more for being over on d'rabonons. Rav Shachter asks this exact question on the gemara in sanhedrin which says "one who violates the instructions of a novi deserves misa beyedei shomayim." So he talks about why that would be true for divrei novi but not for divrei Moshe but in this article he doesn't extend the question to deal with d'rabonons also. I think it must be that it's not literally misa bidei shamayim.