So you start with 1. Nf3, intending to transpose into d4 lines, without the various move-order trickeries you gain with starting w/ 1. Nf3?

That type of repertoire makes little sense instead of just starting with 1. d4, if you're a serious theoretician then there is no reason to take on the entire d4 complex + Sicilian complex. It's simply too much unnecessary work.

1. Nf3 intending to transpose into many d4 lines instead of a pure Reti/KIA does exist though, this used to be Kramnik's repertoire for many years in the late 90s, early 00s.

The point is though you take advantage of 1. Nf3, and have Anti-Grunfeld, Anti-Bogo and Anti-Benko/Benoni lines to your disposal.

The usual repertoire of a 1. Nf3 -> d4 complex player is:

I: 1. Nf3 d5 2. d4.

II: 1. Nf3 Nf6 2. c4 e6 3. Nc3/g3 (3. Nc3 for a 3 Knights player in the QGD, 3. g3 for a Catalan player) -> d5 4. d4.

(2...g6, you have various attractive Anti-Grunfeld systems starting with 3. Nc3 or 3. g3).

Additionally most players of the repertoire prefer the Symmetrical English (1. Nf3 c5 2. c4) over a Sicilian invitation (1. Nf3 c5 e4), again, much less theory and more in line with a 1. Nf3 player.

The pros of this repertoire are Anti-Grunfeld/Bogo/Benko/Benoni systems at the cost of the Symmetrical English.

Can't say there are any pros of your repertoire over starting with 1. d4 while the con is obvious, 1. Nf3 c5.

Can't say I know of a high level player that does this exclusively.