Heck, you can modify a standard Starfleet deflector dish to generate a slipstream conduit, as we saw in VGR. So it's not a total start-from-scratch technology that would take decades to develop. It's more a new application of potentials that Starfleet vessels already have. And some shapes and sizes of vessel are better equipped for it than others.
Starfleet would've needed to have researched the technology further from that point, since as you recall Voyager just made it into slipstream space, but when it did, the stresses were so high that Voyager's integrity field was just
holding the ship together.