A hardcore gym could survive, but you're going to have to do 2 things:
1. ADVERTISE that it is a hardcore place. Aka an ad saying something to the effect like "are you a pussy that likes to wait on grandma's to get done with the bench press or do you want to go to a place for badasses"
2. Make gym membership CHEAP. Personally, I pay $135/yr for a good, public gym. But thats also b/c of the size of city I'm in and the fact local competition is fierce. When I visited Houston, some places like Bally's and 24 Hour Fitness wanted like $50+ a month for memberships. Thats crazy. If you make it cheap, you're going to need lots of dumbells and weights to keep people from getting impatient due to the amount of members. Say Ballys or 24HRF in your area want, say, $450 a year. Charge $150 a year.
3. KEEP that shit hardcore (ties in with #2) - If this is a hardcore gym, and you want to survive, you'll have to keep the membership up. However, the last thing you need in a hardcore gym is a bunch of old people or cheapskates that are only coming b/c of the very cheap membership dues. You need to weed these people out as much as possible. Play nothing but shit like AC/DC, Metallica, Creed, hardcore rap, etc. and make all members sign a waiver saying they wont bitch about the music choices if they contain cuss words. That alone will weed out most of the over-55 crowd. Put up inspirational signs, "No bullshit"-type policy signs, pics of bodybuilders, etc.
If you follow those rules, have a good business plan, heart, and can keep it hardcore, you could make $