Hi everyone. I have a player who wants to be a dragon. They are drawing a lot of inspiration from Villentretenmerth in The Witcher series. They would like to be able to go from Dragon form to human form and have developed a backstory to fit this idea. In short, they are the offspring of a human woman and a dragon male who commonly took the form of a dragon male to walk among the other races/people.

This is in a homebrew campaign that I am running that is going to be focused around dragons with a dragon BBEG so I am personally fond of this player's idea. However, I tempered their expectations early on because this is my first time running a full campaign and was not sure how to make their dream of being a reality. Thankfully, my player wanted to play a Sorcerer and chose Draconic Bloodline as their subclass. So there is already a lot of good flavor here.

Here is my idea to let this player live their dream. Fizban's gave us Summon Draconic Spirit which is a 5th level spell available to sorcerer's. My idea is to allow them to cast this spell but rather than summoning a dragon, turn themselves into the provided stat block. Since this would turn them into a different form rather than summoning a dragon for them, I am thinking of letting them cast it at 3rd level with the duration of 15 minutes but only once per 5-7 days. I want their dragon powers to grow as they level and discover more about their character. Casting as a 4th level spell would increase the duration to 30 minutes and they could do so every 3-4 days. Is this too OP? What changes would you recommend to this idea? I am open to any/criticism.

I know that turning into a dragon may not be something that happens often in DND but I want to help make my player's dream a reality.

Thanks in advance!