You're not getting a Spark (now Vivaldi):
But there are plenty of Android tablets where people have managed to unlock the bootloader. Even the Acer A500 bootloader can be "replaced" ... It voids your warranty, though.
That kind of hacking may not be a proper discussion for these boards, though...
Word of advice with tablets (from experience),... Go with something with Gorilla Glass, or the generic equivalent (called "chemically enhanced glass," or something).