There is a bill before the UK Parliament to amend the ATOL regulations to include any hotels or other such as may be added on up to 24 hours after making a booking. Primarily, this relates to airlines adding on (true) ancillaries onto basic flight bookings.
If the bill is passed then in theory, more people should be covered in the event of a "holiday participant" failure, given the move for people to book more holiday, breaks and other arrangements online.
In practice, it may make matters even more confusing for many and may be criticised as people could start to think that any travel arrangements they make are covered under the ATOL scheme(s).
The biggest issue has to be with with online bookings - specifically, where the actual operator is, who has made the booking. Many websites (online agents and operators) are located offshore (off-EU, even) and even those that are located on the UK mainland may well have an offshore head office, making it difficult to establish if a particular holiday is covered under UK regulations or under the aegis of another foreign land. Then there is the issue of "linked" bookings and ones which constitute a package. I can forsee many arguments arising over the exact timing of bookings; "24 hours" is clear enough - but whose 24 hours?
Of course, the inclusion of airlines coupling on true ancillaries makes sense but we would then need to look at the subject of bonding. Not all airlines make money and airlines are just as likely to go to the wall as anyone else involved in travel. Then, there is the matter of VAT and the Tour Operators Margin scheme. It is also worthy to note that "a package" does not just mean a flight and a hotel. It may also include transfers, car hire, tours and possibly even if you booked an AirBnB or similar rental.
One may venture to go so far as to suggest that if you book and air ticket and then add on a seat reservation and a hold bag - you have booked a package. After all, airlines have gone out of their way to suggest that such things as seat reservations and hold bags are separate from the actual air fare!
In my view, however, the rule should be simple : "If a holiday or break looks like a package, works like a package and presents like a package - it's a package"
The best way to be sure that your holiday is safely booked, with an ATOL company and with proper protection, then, is still by visiting your regular local travel agent.