As TSN describes, it can be done. Work does not end with calculating text block size as the field may overflow it's page. Javascript may also be a stumbling block, the calculations make a trivial call on computing resources when written in C as part of a plugin which may not be the case with Javascript. We also found that Acrobat had (has) quirks depending on the font used. We finally restricted font choice and the use of Rich Text. The latest version of Acrobat may not have these quirks. On the plus side, it makes the design of forms much simpler.
Acrobat do or did have an alternative form system which includes text field resizing, I believe XML structures are used which are not accessible from the SDK.