I dont even think that is the issue for his inclusion. Its the fact that all the third party guests are big gaming icons, how is Shovel Knight going to stand next to Cloud, Sonic, Mega Man, Pac-Man, Ryu and likely Snake?!
Not trying to down play the guy, as I really love Shovel Knight myself
. But like a poster said already, he is likely got get a Mii Sword Fighter Costume and/or a Smash Trophy instead.
I would like for him to be the playable indie rep, but I would rather that honor go to Shantae; the series is more or less Nintendo exclusive and always found home on Nintendo Handhelds (GBC, DSi, 3DS) and Wii U (Half-Genie Hero next year, port of Pirates Curse). Granted, the series is getting its first multi-console start with Half-Genie Hero next year but point still stands; she is linked closer to Nintendo then Shovel Knight is.
But I don't expect her to join Smash either, even though that would be a really pleasant surprise
!
And the point about link to Nintendo completely was tossed out the window when Cloud was announced for Smash so who knows honestly
.