Thought it would be fun to do. Based on market performance (NOT game library): 

Sony Playstation 4:

North America: A, Europe: A, Japan: F

Sony Vita:

North America: F-, Europe: F, Japan: C

Nintendo Wii U:

North America: D-, Europe F, Japan: F

Nintendo 3DS

North America: C+, Europe: C+, Japan: A-

Microsoft XBox One:

North America: B-, Europe: C-, Japan F-

Polish grades ? xD

Based on what?

what's wrong with 3ds??!?

Market performance. 

Sony Playstation 4:

North America: A, Europe: A, Japan: B

Sony Vita:

North America: F-, Europe: F, Japan: C+

Nintendo Wii U:

North America: B, Europe B, Japan: B+

Nintendo 3DS

North America: A, Europe: A, Japan: A

Microsoft XBox One:

North America: B+, Europe: B, Japan Z-

Sony Playstation 4:

North America: C, Europe: B, Japan: F

Sony Vita:

North America: F, Europe: F, Japan: D

Nintendo Wii U:

North America: B, Europe B, Japan: A

Microsoft XBox One:

North America: B, Europe: C, Japan F

Wat?

first of all, you give the Wii U a B+ in japan, but the PS4 an F. How is that justified?

Second of all, how the heck does the Wii U get the same score in NA as the XBO?

Sony Playstation 4:

North America: B, Europe: A, Japan: D

Sony Vita:

North America: F, Europe: D, Japan: C

Nintendo Wii U:

North America: C, Europe C, Japan: B

Microsoft XBox One:

North America: B, Europe: C, Japan F

lol, Wii U doesn't sniff a B anywhere for its market performance.

That's like that lazy student who thinks he/she is entitled to a decent grade because they're a "good person" but their assignments/test scores are all well below par.

No free passes for past legacies, Nintendo doesn't deserve a good grade for the Wii U plain and simple. The D- for North America I gave them is probably a bit generous actually, they could easily have a full on F in North America and deserve it fully. 

Bad sales almost constantly, bad execution, no marketing/mindshare, no momentum, terrible release schedule, terrible third party support. That doesn't get you a B-grade, sorry.