Depends on what you consider 'substantial'. Jack is probably 6th, 7th or 8th in line (so higher up than Eugenie is to the throne
but I think we can agree it is highly unlikely that she will be queen one day) - however, given that the baronetcy is only passed on in male-line, I would say the chance that Jack will be a baronet is small but the chance that baby Brooksbank will be the baronet is a lot higher - nobody needs to die for that to happen. There is no confirmation that either of Jack's cousins higher up in line have children. So, baby Brooksbank might be the highest up in his generation!
If these three cousins don't have children or only daughters, baby Brooksbank would be the baronet of his generation. Given that Jack's first cousins are already in their early forties and his second cousin, the heir-apparent, is 38 and according to The Peerage neither of them have children; it isn't that unlikely to happen (note: of course it could be that one or more of them do have sons but no information is available to confirm that).
See line of succession to the Baronetcy (based on information available on wikipedia & The Peerage - but could be incomplete) included in the overview below:
Male line descendants of the 1st baronet - N.B. numbers refer to real spot in family order (colors indicate generation):
Sir Edward Clitherow Brooksbank, 1st Bt (1858-1943)
1. Stamp Brooksbank (1887-1915; KIA)
2. Edward York Brooksbank (1888-1935)
2.2. Edward William Brooksbank, 2nd Bt. (1915 - 1983)
2.2.1. Sir Edward Nicholas Brooksbank, 3rd Bt (b. 1944)
2.2.1.1. Florian Thomas Charles Brooksbrank (b. 1982) - HEIR APPARENT (LoS 1)*
2.3. Benjamin John Brooksbank (b. 27 Sep 1918) (LoS 2; if still alive at age 102)
2.4. Stamp Godfrey Brooksbank (1922 - 2017)
2.4.1. David William Brooksbank (b. 1946) (LoS 3)
2.4.1.1. Scott Brooksbank (b. 1976) (LoS 4)**
2.4.1.2. Charles Brooksbank (b. 1979) (LoS 5)
2.4.2. George Edward Hugh Brooksbank (b. 1949) (LoS 6)
2.4.2.1. Jack Brooksbank (b. 1986; son of 5) (LoS 7)
2.4.2.1.1. Baby Brooksbank (b. 2021; son of 6) (LoS 8)
2.4.2.2. Thomas Brooksbank (b. 1988; son of 5) (LoS 9)
2.4.2.2.1. Wilfred Brooksbank (b. 2020; son of 8) (LoS 10)
4. Hugh Godfrey Brooksbank (1893-1914)
* The heir apparent
got engaged over 6 years ago, so it's quite likely that he is married an might have children... However, I didn't find any information on a wedding nor children.
** He might have a son 'William Emile Brooksbank (b. 2009)'; if the Scott in
this birth announcement is Jack's cousin - in that case baby Brooksbank would be the second of his generation... but about 12 years younger, so he still might be a future baronet depending on whether this William Emile would have any sons...