This is my take as well. The expectation was for Beatrice, as Prince Andrew's oldest child, to be a full-time working royal, while Eugenie was free to pursue her own interests, yet available to be called upon as needed. At some point, probably when Beatrice was a pre-teen / teen, the decision was made that children of spares would not be called upon to be full-time working royals. I suspect that it was not accepted as a fait accompli in certain quarters.
What intrigues me is the money part. Right now the BRF is funded by the Sovereign Grant, the Duchy of Lancaster and the Duchy of Cornwall. The funding scheme for the Sovereign Grant is 15% of the Crown Estate income (it is temporarily 25%) and my rough calculation has it trending at £50 million. The funding scheme for the Duchy of Lancaster and the Duchy of Cornwall is that their respective beneficiaries get paid the net income from the duchies which has been trending at about £20 million per year for each duchy.
Technically, the income from the duchies is available for their respective dukes to use as they please, but Queen Elizabeth and Prince Charles have used the income to fund BRF activities and needs that presumably are not covered by the Sovereign Grant and other sources, but I have no doubt that they have been able to amass considerable personal fortunes from their duchy incomes. So fast forward 30 years and instead of a BRF of 10-15 working royals being funded by 2052 equivalent of £90 million, you are going to have 2-4 working royals being funded by the 2052 equivalent of £40 million plus the Sovereign Grant, and if the Sovereign Grant remains 15% of the Crown Estate income, then that is 2-4 working royals being funded by the 2052 equivalent of £90 million. If it plays out that way, I boldly predict that there will be a bit of an optics problem.
Of course reasonable arguments can be made that, at most, the working royals should be the monarch, consort, adult heir and spouse. However I can see there being other royals being tagged in to "provide services" to the UK and the Commonwealth, and implicitly to justify the funding that the BRF receives.
What I think should be happening is that children of spares should be raised with the expectation that they are free to pursue her own interests, which is pretty much happening, Princess Beatrice is the last royal who was probably raised that way and she seems to have adapted. However that does not mean that if there is a need and mutual agreement that one of these royals cannot be conscripted to become a part-time or full-time working royal, rather the point is that their upbringing should not be geared that way.
The toughest nut in all this is what about non-heir apparent children of monarchs / heirs apparent, e.g., Charlotte, Louis. Presumably they are being raised to hold the monarchy and service in high regard, but I don't think that they should feel duty-bound to become working royals, however as noted above, if there is a need and mutual agreement, I don't have a problem with them being working royals, and I think that a benefit to having a small bench of working royals carrying out duties, in addition to the monarch, heir apparent and their spouses, does help justify the tens of millions of pounds that the BRF gets from the Sovereign grant and duchy income.