A few days ago I did a post on the difference between the Heir Presumptive and the Heir Apparent, and how that relates to Bridgerton. In that post I explained how Benedict was the Heir Presumptive, but he has since been displaced due to the birth of Kate and Anthony's son, (whom I will call Edmund). I believe that this is something that should be playing a part in season 4 as Benedict regains his purpose in life, and navigates no longer being Anthony's heir.
Image Credit: Netflix
Over season 1 and season 2 Benedict developed his art and explanded his social circles to include more artists. In the background of Benedict discovering himself was always the knowledge he was Anthony's heir, this was very much a part of season 1 when Benedict realised he might have to take over if Anthony was killed in the duel against Simon. By season 2 Benedict was exploring his art more, and looking at taking it further by applying to the Royal Academy, this sense of moving forward and away from responsibilities could have been prompted by Anthony's decision to marry, which could lead to him gaining an heir and releasing Benedict from the responsibility. However, by the end of season 2 Benedict had become disillusioned due to Anthony's intervention, and he felt that his place in the Royal Academy was bought and not earned, leading Benedict to give up his art. Ideally this should have been the shift into Benedict's season, but the production had a different idea, and come season 3 we saw Benedict straddling two senses of self, the first as he filled in for Anthony finding some purpose in running the estate, but also we saw him experimenting in his personal life, setting him up for how he starts season 4. 
Image Credit: Netflix
In the advanced screening of episode 1 (which will be released in an hour or so as of writing this), we see Benedict moving further from duty and purpose towards a lifestyle of reckless behaviour and self indulgence. This change for Benedict is something that could have been prompted by the birth of Edmund, who is now Anthony's heir. Benedict has been displaced as the heir to the Viscountcy by the birth of Edmund, and while he may not have wanted to be the next Viscount, his displacement will have impacted him as he has lost his place in the world. Violet makes a comment about Benedict's behaviour over the previous month, this is a timeframe that likely coincided with when the family received word of Edmund's birth, confirming to Benedict that he was no longer Anthony's heir, this is reinforced by Benedict reminding his mother he is the second son. Benedict reminding Violet he is the second son is said with frustration, and perhaps a little bitterness, because for him it is a reminder that his place in the world for the last 10+ years, as Anthony's heir - no matter how unwelcome it was - is now lost, but I think this could also be a catalyst that helps him to return to his art.
Image Credit: Netflix
From stills released it is shown that Benedict starts to sketch again after he has met Sophie, as the Lady in Silver, and while she is the one that inspires him, and becomes his muse, it is possible that he becomes more open to looking at art again for his path in life due to the birth of Edmund.
We can only speculate on how much, or little, Benedict's sense of self and purpose in life is tied to his position as the second son, the heir until the birth of Edmund, as this is not something I feel the show will explore too deeply. It is possible that Benedict, has felt a sense of duty while acting on behalf of Anthony, but has confused this with a sense of purpose, leading to him losing sight of who he is. The birth of Edmund, and then meeting Sophie has given him the freedom, and the inspiration, to return to discovering what his true purpose in life is, and allowing him to become his true self.
