An interesting pet opening I discovered, what are your thoughts?

So this pet opening arises after the moves 1. e4 g6 2. d4 Bg7 3. Nf3 d6. The opening starts with 4. e5 !?. Everybody and their mother will play dxe4 here so I will discuss that line. After 4. ... dxe5 5. Nxe5 Bxe5 6. dxe5 Qxd1 7. Kxd1 we arrive at this position:

So the idea behind losing the right to castle here as white here is it will be really hard for black to not lose the right to castle as well, his knight on the kingside is not going anywhere any time soon (and so does the rook) and on the queenside, you have ideas of Bb5, Rd1, Nb5. On top of that, you have a great dark-squared bishop and an annoying pawn for black to deal with.

Here is an example game I played yesterday, where black decided his knight is going somewhere sometime soon by playing e6 and strengthening my bishop even more (I am pretty low rated so I know it's not the greatest of games, but still a bit unusual and fun to watch I think):

Playable but suboptimal.  Black has probably a slight advantage. 

Agree, of course, Bxe5 is horrible, and no reasonable pirc/modern player would play it. 

As a Pirc player who plays Pirc ideas even when white, I would never voluntarily give up 0-0, since a fianchettoed bishop with 0-0 behind it is fundamental with my play.

Back in Fisher's time, not castling was worse than queenside castling, a show of weakness in fundamentals.

If you KNOW that the opening will confound and disturb your opponent, by all means, have a ball. Generally Kxd1 causes more trouble than its worth. 

At the risk of sounding redundant...

5...Be5? makes no sense.  Instead 5...Nbd7, and black is fine.  He has the lead in development, thanks to white moving the knight twice, and quite possibly again.  Pressure along the h8-a1 diagonal, in addition to hitting the d4 pawn.

yeah, you are right... I just assumed Bxe5 when this line may even seem unreasonable for black when Nd7 is possible. To my defence, this is the best move according to Stockfish

Yes, you can check for yourself... My guess is that it values the immediate consequence of white not being able to castle more than the long-term strategic ideas of the bishop on g7 just because of the nature of such engines.

I would assume that analysis wasn't done at very deep ply; and that's perhaps the biggest 'risk' of 5....Bxe5. Anyone can subjectively look at white losing his castling rights and consider black to be better, only to find out a few moves later that it's black who's in trouble.

In essence, if you fiancietto in the opening you don't give up the bishop for a knight, the only exception is the Dzindzi Indian. In an Accelerated Dragon I took on c3 recently, which disrupted white greatly, yet I still lost (and that was without the white darksquared bishop on the board): mind, the trade itself was the best idea but asked for active play from black which I did not immediately do.

Annoying double posts due to browser delay.

Just another example of why you do not blindly trust what engines throw out.

What is the motivation for white to play 4 e5?

Seems anti opening principles to me

No good player will take the knight and give his dark bishop in that position.

 but most of his opponents will and that is all that matters

Sf gives 5...Bxe5 as its second option, behind 5...Nh6 and ahead (not really, almost the same eval) 5...Nd7, so Bxe5 is not horrible at all, and could be the option if the black player likes endgames (but then he wouldn´t probably had chosen 1...g6 against 1.e4)

Im gonna ask the obvious question..."Why" does stockfish like 5...Be5.

The Bg7 is a monster, but the Ne5 also, so you don´t exchange one bad piece for a good one, but two good, in addition you prevent white from casling, that is the positional explanation, maybe SF has tactical reasons as well to prefer that move

Black is moving 7...Nc6 and castling queenside. 8 Bb5 Bd7 9 Re1 O-O-O 10 Bd2.

I dunno, it seems like black needs to make a bunch of moves you expect him to for the opening to work ?

It may work well at lower levels, but you should focus on openings that can maintain White's advantage for a longer period against the higher ratings you hope to achieve and lead to solid middlegame strategies.