Then there's always the infamous dialogue from "Little Green Men" that might be taken to indicate that Quark, displaced to 1947, would be able to sell warp drive to the Vulcans and the Klingons as a novelty item.
Of course, that need not be taken as gospel (even though it is canon, hallelujah) because Quark could be confused, speaking in hyperbole, or then counting on further exploiting his newly found ability to travel to the past.
As for whether discovering warp is difficult or easy, TOS already seemed to think of the Prime Directive in terms of "a species is worthy of contact in equal terms only if it has warp drive and dwells among us". It was never spelled out there or in any of the later spinoffs, of course. But the implication was that there would be some species to which the PD did not apply, species that already knew about the interstellar community. And that Catch-22 could not be solved unless such species had the ability to develop interstellar travel by themselves. And yes, even TOS seemed to very much go by the idea that sublight interstellar travel was impracticable or impossible (except when it was a plot point in "For The Title Is Long").
Timo Saloniemi
Of course, that need not be taken as gospel (even though it is canon, hallelujah) because Quark could be confused, speaking in hyperbole, or then counting on further exploiting his newly found ability to travel to the past.
As for whether discovering warp is difficult or easy, TOS already seemed to think of the Prime Directive in terms of "a species is worthy of contact in equal terms only if it has warp drive and dwells among us". It was never spelled out there or in any of the later spinoffs, of course. But the implication was that there would be some species to which the PD did not apply, species that already knew about the interstellar community. And that Catch-22 could not be solved unless such species had the ability to develop interstellar travel by themselves. And yes, even TOS seemed to very much go by the idea that sublight interstellar travel was impracticable or impossible (except when it was a plot point in "For The Title Is Long").
Timo Saloniemi