George V followed the (pre-Revolution) French standard under which the Royal House consisted of:
1. The King and the Queen Consort.
2. The monarch's legitimate children.
3. The monarch's legitimate grandchildren in male line.
4. The legitimate children of the eldest son of the heir to the throne.
5. The Queen Dowager when applicable.
In addition, wives of royal princes were also members of the Royal House by marriage whereas husbands of royal princesses were not.
With the introduction of equal primogeniture, the list above could be modernized to include all legitimate grandchildren of the monarch (in both paternal and maternal line) and all royal consorts and widows/widowers, either male or female, which is close to the Belgian system now (with the exception that, in Belgium, all grandchildren of the heir are also members of the Royal House).
I doubt that they will go to a broader number of royals. They are trying to reduce the number so they will be reducing who is royal to the children of the monarch and the children of the heir apparent.
The public don't want Beatrice and Eugenie as royals so there is no way they will want to see that number expanded again (last time I was in Britain I asked numerous people their thoughts on the York girls and no one had a good word to say about them).
I don't see a need for a minimalist Royal House, as in Spain or Norway today for example, as long as public funding is limited to the monarch, the monarch's consort, and the heir (and his/her consort), while other members of the Royal House get reimbursed only for official duties they perform. There could be public funding also for the dowager or former monarch upon abdication, which is fair.
You are advocating expanding the amount of money spent by the taxpayers on the royals. Other than the Queen and Philip the rest are funded from the private incomes of the Duchies for their official duties not from the Sovereign Grant.
There won't be an abdication in the UK - unless William decides to do so, which I can see him doing - but neither the Queen nor Charles will ever abdicate. They believe they are there for life. If they do decide to abdicate they should get nothing as they have given up their duty and no moneys at all should be paid for that.
The spouse of the previous monarch is covered in the Sovereign Grant now so no increase there.
The streamlining of the royal family is clear for anyone to see if they look at the way the York girls are sidelined and so the family is going to have fewer workers doing fewer engagements - in line with the reported, but never confirmed, ideas that Charles wants a smaller royal family. The fact that that has been repeated over and over again makes it virtually impossible now for anyone to go back.
We have already seen The Queen change the LPs with Edward's children by the use of Her Will which would suggest a future where they LPs themselves will be changed to reduce rather than expand the number of HRHs as you are suggesting.
If all the grandchildren of a monarch were HRHs then by Christmas this year there would be 36 HRHs compared to the 21 we will have. That number would also only increase as Harry has children. The intention though is to reduce that number not add to it.
I would even go so far as to say that HRH should be limited to the first 6 in the line of succession - regardless of relation to the monarch and so people would lose it as others were born - as they do the need to ask permission to marry.