Another useful feature for Google Base would be to allow "simple" structure to be added to Attribute Types. In this simple structure, readers (i.e. Google Base) are free to move the inner structure elements "up a level" with the net result that there would be no change needed for their DB model.

For example, here's a "location" (from here):

<g:location>
1 Bank Street
Ottawa, Ontario
Canada
</g:location>

I propose they also accept: 

<g:location>
    <g:street-address>1 Bank Street</g:street-address>
    <g:locality>Ottawa</g:locality>, <g:region>Ontario</g:region>
    <g:country-name>Canada</g:country-name>
</g:location> 

The 'location' attribute gets stored exactly the way it would be in the first case (we strip the inner markup) BUT we get the additional benefit of the all the new attributes AND we don't have to throw away information we already know!

One could also see this being used in the proposed "person" attribute: 

<g:person>
    <g:given-name>David</g:given-name> <g:family-name>Janes</g:family-name>
</g:person>

Note that the new attribute names I'm using are based on the vCard standard.