With the large number of changes coming in A17, retaining data from a previous save has a 98% chance of failure. We won't be able to tell you 100% until it releases, but based on known information this is pretty accurate.
This has been the case for most of the recent releases. In earlier alpha's it was sometimes possible because there weren't a lot of changes being made to the blocks data file.
This time around, the game is being put on an entirely new version of the engine. It's allowing the devs to improve optimization, and greatly removes previous limitations in the file structures that prevented us from having item/block counts over a certain number.
As a result of these changes, I would imagine that the current data storage for this information will become completely obsolete. Or, it will be re-designed and re-structured to a level that is not compatible with the old format. (Which basically makes it obsolete anyway.)
Only time will tell, but a general rule with games in early development like Alpha is that a complete wipe and restart is required.
Thanks to the way they have it set up though, you can choose to stay on a16 and play your current map without upgrading. You just won't be able to experience any of the new features.