If you look at the overall track record Square has with their Final Fantasy games and DLC, they've been very reluctant to have any DLC. XIII-2 was the first one that offered any DLC and Lightning Returns had nearly none and XV has already been promised that it's going to be a game with no DLC plans. So I think you're save from VII having DLC like you describe. DLC exists as a way to recoup the development costs in an industry where the price of games hasn't changed since the PS2 era, yet the cost of making games has skyrocketed.

VII will likely end up costing more than $100 most likely after all the parts are out. But the way they are talking you're getting an even more grand and epic game than the original VII. There's going to be even more content to explore and new stories with likely a cleaned up narrative. Square isn't just updated the visual for VII because that game already exists. If they're going to remake it they want to do right where it will be worth replay for old fans so that they have something that they haven't seen before.

So I think it will be fine. It'll cost more to play the game, but you'll get more game as well.