The main advantage of blowguns - range - has been reduced somewhat in recent years due to the increased effective range of stock Nerf blasters. However, I can see them as still being a viable niche weapon.I agree with the above short of the blowgun's main advantage not being range, but accuracy. The reason I have incorporated a blowgun into pretty much every loadout of mine since '13 has been because of its ability to conserve ammo by requiring less pot shots. Its the only piece in my arsenal(or anyone that I know for the matter) that can consistently(roughly 80%) make tags 30 yards out. Not to say there aren't well-modded blasters that can't do the same with a much higher and steadier ROF but again, these are 'well-modded'. The best use for a blowgun is either secured onto the top rail of your primary or attached to a sling of some sort for easy carrying.
"Why not to use a blowgun as a primary?":
Blowguns can be(...)awkward and potentially teeth-shatteringly unsafe to use at close range.That and the fact that 9 out of every 10 people use a blaster that uses mags, so the prevalence of whistler and buzzbee darts are starting to die out. Less people using these types of ammo means theres almost no such thing as scavenging ammo with a blowgun(atleast in my meta I've been noticing).
Overall, I'd say they're still relevant and have a place in games but there are risks that need to be accounted for before deciding to go out and "spittin' dat foam".