I'm far from convinced that any heritage operate needs to alarm themselves unduly. The ORR are almost certain to want them to do it eventually but one thing that comes across clearly from the judgement is that the ORR don't want to drive anyone out of business to comply. They appear quite willing to grant extensions to any deadlines where there is a planned scheme of a work with a fixed end date. If WCRC had been applying for an extension on the basis that they needed more time to fit their stock because they had a scheme but it was taking longer than expected, they needed to spread it out over another season for financial reasons, or similar I would not be at all surprised to discover the ORR would have looked favourably on that. Instead WCRC seem to have taken the view that they should be exempt, completely, from any requirement whatsoever. I would suggest a heritage railway with an eye on the future should start thinking about coming up with scheme to fit their stock with CDL over the next few years or so. Then when the ORR do start making moves in the direction of requiring it on heritage operations they'll already been in a strong position. Particularly if financial or practical considerations mean they need to ask for a bit more time to fit their fleet.
Nothing I've read suggests that this is the death knell for heritage operations or indeed mainline railtours.