The guys at B & H tell me that the 3880 will be out soon, though no one will actually say when.
They are talking out of their hats...
If they DID have certain knowledge from Epson, then they would be violating their NDA by saying there will be a 3880 out soon. Epson has made no statement to the public, one way or the other.
What they "may" be saying is they "think" there will be a 3880 soon. That's a different story. But unless they define "soon" as next year some time, then again, they would be wrong. I'm not at liberty to say one thing or the other (due to NDAs) but I will sat=y that if you want the 880 inkset in a small format printer, the only one currently available is the 2880 which has the Vivid Magenta and new dither technology (only seen so far in the EPson 11880).
As for the Vivid Magenta importance, it will help any colors in the magenta section of the gamut including blues and purples as well as magentas and reds. If you don't use those color at near maximum gamut of Adobe RGB or ProPhoto RGB then you won't see any differences between K3 with and without Vivid Magenta. If you do use those colors on a typical basis and you are working in PhoPhoto RGB, then the Vivid Magenta will be an important consideration.