GRRM's intentions: Discrediting the trial of combat?

[Jon Weirgaryen]

And if the new ruler wants to observe formalities, Tyrion could simply be pardoned.

They might have to. Depending of the Iron Bank's goodwill (and you can tell, they are not in favour of current Lannister rule), the Iron Throne might need the upcoming power of the papermoney and paper deeds of "Bank of the Red Shield"¹ that does their deeds & money-by-mail service through the Second Sons.

Much more reliable and safer then the faceless men, don't you think?

It does sound very crackpotish when you think about the first time. It makes sense if you take into account the way the world works. The fun part is that Tyrion is absolutely unaware of what he really has kicked off.

1) The Lanninsters show a golden lion on a red shield, don't they?

[tl;dr]

Tyrion will be pardoned.

[Talking Hodor]

Whose head is Qyburn going to sew onto the Mountain that Can't See Because his Skull's in Dorne so that he doesn't bump into any walls during the trial by combat: Tywin's, Joffrey's, Robb's, Eddard's? Granted there's no lack of heads piling up in King's Landing, but which one would be the most intimidating?

[Jon Weirgaryen]

Hodor?

Whose head is Qyburn going to sew onto the Mountain that Can't See

You are most certainly talking about Ser Robert Strong. Do we know he cannot see? I haven't reread that part, but I do not remember an impediment.

In your question you mix together the implication that Ser Robert Strongs body once belonged to the Ser Gregor Clegane and that the actual head of a now left headless Ser Gregor Clegane was sent to Dorne. That all does make a lot of sense.

Though a head was sent to Dorne, we cannot actually rule out that it was not taken from some collection of heads and Ser Gregor still is tightly connected to his own. As said above, he may or he may not. In case of a missing head, there are the options that Ser Robert has no need for his own eyes to see, either because of some remote control a la Melisandre or he might be remote championed by an even higher power. As to those two suggestions I cannot present any lead though, so forget if you dislike.