There are many things I really don't like about Sport, but one of the few good things it has done for me is to solidify my faith in PD in how they handle DLC.
I agree with the argument that we "deserve" the free DLC because the base game is so barebones to the point where it felt incomplete. I think Sport was sold with the promise of a consistent stream of free content. But what little has been put up on sale, I really liked their implementation: Sport being a competition focused title and not an RPG, we were given an option to buy most cars with real money to skip the grind and get right down to the competition. I really appreciate how we can even turn off the option to pay with real money from appearing at all in the Options menu. The impression I get in the OP is that there should be a season pass where players can get exorbitantly expensive cars quick and easy, but I feel that that's more a problem with GT Sport's current economy that's more easily solved within the confines of adjusting in game payout rates than involving the sensitive and controversial DLC. Heck, I don't even know why we aren't allowed to buy the unicorn cars with real money; you'd think a system like this would be used mainly for these horrifically expensive cars.
In terms of car and track DLC, the quality of both have been astounding, and I daresay GT Sport has the most accurate models of any modern video game. They truly cut no corners, and the models are supposedly future proofed, cut in poly count for the PS4. Seeing this quality in the cars, and with the recent Spa and Glickenhaus licensing debacle, I almost feel guilty for receiving all this for free, even if the game in which most of these cars are used treats them like garbage.
That all said, I'm still going to vote "No" for paid DLC. PD has been historically proven to have horrible communication to their fanbase, and I feel that to sell DLC in a game, the devs or a representative needs to communicate with the player base to explain how it works, why it's there, and why we should pay for it. Invariably, the question of "why isn't this content free", and "has this been withheld to be paid DLC from the main game?" will arise. Can you imagine if PD sold us new DLC for Sport, like a 0-400m acceleration test from previous games? It'd be eye watering new content, yes, but it's a feature so basic you'd wonder why it wasn't in the game to begin with. PD just strikes me as that sort of oddball company, and I don't think it can handle the communication aspect of selling DLC well. And honestly, if I were the developer and tried to rectify the omission of an acceleration test, I wouldn't want to come under fire from the mostly unappreciative fanbase. I would want to make content for such a fanbase if subject to that kind of abuse (see: every GT7 thread that has devolved into an off topic toxic poop slinging storm).
While I do very much want to pay for new cars and tracks in Sport, I do appreciate that everyone who has the game is on an level playing field; a very basic requirement of a competition focused title. Can you imagine if Spa and/ or a Fugu Z popped up in an FIA race, but you can't practice for it if you didn't buy the car and/ or track? Or if a DLC exclusive car happens to be the meta car? Even if GT7 claims to be a more traditional title focused on Single Player, a level playing field makes it more of a traditional game to me. Personally, I can only see DLC working is in aftermarket parts, paints, or wheels in the livery editor.
Lastly, while I'm also very much for paying for new content to incentivise creating new content for the game post launch, we need to have a lot of faith in the developers. I'm apprehensive about paid DLC as a whole for video games, not just GT7. The one big example I will cite for this is GTA V: GTA Online generates so much revenue for Rockstar, and supposedly has such a bigger return in investment, they'd rather keep pumping out new content for GTA O rather than to make a GTA VI, when GTA V is seven years old at this point. There was even supposedly DLC for single player that wound up being scrapped and repurposed for Online. I don't want to see GT7 set a new trend where such practices start and are tolerated. And I don't trust any big company, or its fanbase for that matter, to not support such practices.
I just don't think either PD, or gamers as a whole, are prepared for paid DLC.
tl;dr: No. Hell no.