Which are the ideas in the Van't Kruijs Opening? In a game with a friend, he made a really unexpected move, e3:

[FEN "rnbqkbnr/pppppppp/8/8/8/4P3/PPPP1PPP/RNBQKBNR w KQkq - 0 1"]


Afterwards, when analysing the game I found its name is Van't Kruijs Opening and I was wondering which are the ideas to play it.

For white, this seems a passive move, giving advantage in the centre to black. But on the other side, like e4, it opens the way to the King's Bishop and Queen. It can also lead to aggressive variations like the Keoni-Hiva Gambit, where white sacrifices a pawn for development, which seems dangerous.

[FEN ""]
1. e3 d5 2. Nc3 e5 3. f4


Could you confirm/refute this analysis? Could you discuss other ideas?
White can transpose to the Stonewall or the Colle systems after 1...d5 or if 1...e5 attempt a reverse French.

Otherwise 1. e3 is a move which needs no attention or search for ideas, because there can be none.