I don't know: a French Defence with a move in hand has to have some merit!

Agreed. I have occasionally played this as Black - an Owen defence (1.e4 e6 2.d4 b6!?).

Nd7 is playable but bloks in the lsb, f6 can be dangerous and compromises the kingside castling, Nc6 is countered by Bb5...

So what's the thinking behind white's move? Well, just guessing: "after the c6 pawn has been removed, B is somewhat vulnerable on the white squares, so b5+ seems good. But he has the lsb to interpose, and nothing happens. What if it is the Q instead who gives the check? He can't use the B or Qxb7, and if he uses the N to shield, I'll have time to play Qxd5!". So this move inmediately threats d5. The problem is that after something dull like a6, the WQ is very badly placed for nothing.

White can't allow his Q as it stands. This move was surely part of his plan of developement: make room for his lsb.

Blsb is tied to the defence of b7.

Nc3 would have caused black to worry a little about how to defend d5. If d5, white has a target after the exchanges, and maybe better chance to free his pieces. I can think the reason behind this move: White wants to play Bd3-c2 and doesn't want it exchanged by Nb4. Black can't easily go e5 without opening the diagonal to Wdsb. Note that the Q pin is not a problem after a6-b5, and the WQ loses tempo moving around. -

Now, 8... Bd7 instead threats Nd4, Qd3 (only one to prevent Nc2+), Bf5! and black wins: (8... Bd7, 9. Nc3?? (say), Nd4, 10. Qd6, Bf5 Sadly, it seems that after Bd7 white's only defence is the humilliating 9. Qd2!

Very interesting, but after Bd7 can white get away with taking the pawn on b7?

This is just not coherent with the Kside plan. g3 (for Bg2) was more sound, but white has to "solve" its Q's problem before black goes for it.

White must be noticing by now that Black has got all his minor pieces in action - albeit restrained at the moment - all centralised to boot, the King castled and the rooks connected. Black also has the big share of the centre. He probably won't have seen the tactical threat this bishop development represents.

There is a stage when you play just moves that seems good for some reason, disregarding "principles". I support not to stick to principles without knowing why, but here you can see an almost trapped Q and the undeveloped pieces unable to help, period! Ok, now, look at the guy's rating.