Rails 6's implicit_order_column is great but wouldn't it be even more great if it worked for more than just finders (e.g. first, last)? It's reasonable to expect, after declaring an implicit order column, for it to also be in effect when using other methods (e.g. all, take, pluck, each, associations) — but it is not.
IMO default_scope is not really a substitute, either, unless you want everyone else to always have to remember to call .reorder if a different order is needed. In my view, scope is more of a filtering thing than an ordering thing anyway, and I always wish there had been an analogous order macro.
I think implicit_order is needed (taking a block, not just a column name, so that direction or joins, etc, can be specified). As soon as a different .order is called, this one should be dropped entirely.