Unix/Linux is for winners.
1st place: Debian (type of linux) (linux: unix variant class of os's)
2nd place: CP/M
3rd place: Windows
4th place: ios
5th place: osx (bleh yuk)
Bluntly put, no, it can not replace a tablet.
Well it depends on what you're using a tablet for.
so, if you want something that wastes your money and space without doing anything useful, the 3DS probably isn't worth it.