i'm up for it :-)
Whatever happened to the Sicilian Scheveningen?

I think you've kind of alluded to the reasons yourself there. I basically play the Scheveningen (sometimes), but I do it via the Najdorf move order with 5...a6, and e6 only on the subsequent move. It was Kasparov who popularized that -- a6 is a useful move in any case, retains flexibility/hides your intentions, and most importantly avoids the Keres attack. I've not encountered that Be3/g4 line you mention.
Problem with the Schev is that the Keres is very effective against it, so you probably see A LOT of 5...a6 manuevers. If you played the English attack it wouldn't matter that much to you, but if you insist on a Keres, then no dice.

Spiffe, I've heard that the Scheveningen is one of the more positional variations of the Sicilian. Do you think that that's a fair assessment? Is it a good first variation to learn with the black pieces?
Yeah, I guess I'm a Schveningen player with a Najdorf move order (5...a6). Or maybe I'm a Najdorf player who likes Schveningen structures (...e6) rather than absolute Najdorf structures (...e5).

Spiffe, I've heard that the Scheveningen is one of the more positional variations of the Sicilian. Do you think that that's a fair assessment? Is it a good first variation to learn with the black pieces?
I guess it depends on what you mean by "positional". If you mean a game characterized by complexity & a need to judge the best course from among several possibilities, I'd say yes. If you mean a quiet game that's not likely to explode in a tactical flurry at any time, then the answer is most definitely no.
/shrug, I've always found it pretty solid and straightforward to play. That's not to say that there aren't hairy lines that require precise defense, though that seems to be the case in almost any Sicilian. Your mileage may vary.

I have only faced a few pure schveningens (not through Najdorf move order) in the two years that I have been playing chess. I think a lot of people are afraid of the Keres attack, which the Najdorf move order avoids. The few times I got to try out the Keres attack I never really got an edge, but that is probably because I didn't know the theory and never got any practice with it. Recently, however, I read somewhere that black is doing really well in the Keres attack.

I play the Scheveningen structure with the 5...a6 move order as well. Doesn't avoid the Keres idea (g4!?) since the Perenyi attack comes after 6...e6 anyway. That's what I tend to play against my own Sicilian of choice as white as well.
For reference, here's one of my modest attempts (PS I'd like to have a few games if you're interested in going over this system)

I have adopted the following move order vs. the Schev.
what if he / she takes the pawn?

I have adopted the following move order vs. the Schev.
what if he / she takes the pawn?
On g4? Her majesty dines on horse stew.
I suppose Black can regain the piece after 7... Nxg4 8. Qxg4 e5 9. Nf5 g6, but then 10. Nd5 looks horrible for black.
Hey y'all,
I am a very big fan of the challenging lines in the Open Sicilian. Against the Najdorf and Richter-Rauzer, I play 6.Bg5, the Dragon I use the Yugoslav, and the Scheveningen I like 6.Be3 a6 7.g4! going for either the Perenyi piece sac or transposition into some of the more dynamic Keres attack lines. Still, I run into the Najdorf every other Sicilian game, the Dragon every 4th or 5th, and plenty of Richter-Rauzers, but only one Scheveningen here at Chess.com.
I know Shirov gave the Scheveningen a beating a few years before, but I doubt even that many people here are that into opening theory study. In any case, does anyone want to provide an explanation for the decline in popularity or, better yet, challenge me to a game where I could put your Scheveningen chops to the test?
Cheers,
Doug