I've started a thread in the EE forums:
http://ellislab.com/forums/viewthread/244991/
There has been one solution posted, but it requires a hack to the native EE text fieldtype code (/system/expressionengine/fieldtypes/text/ft.text.php) from
$field = array(
'name' => $this->field_name,
'value' => $this->_format_number($data, $type),
'dir' => $this->settings['field_text_direction'],
'field_content_type' => $type
);
to
$field = array(
'id' => $this->field_name,
'name' => $this->field_name,
'value' => $this->_format_number($data, $type),
'dir' => $this->settings['field_text_direction'],
'field_content_type' => $type
);
But I don't know what impact that would have to the system. I've posted the question to the developer, and will update the thread if there are any other solutions suggested.
Thanks Derek for jumping in on this. I don't have enough reputation points to add a comment to your answer, so I'll just edit my entry.
The hack was required in addition to the function change suggested by the developer log to make the add-on fully functional.
Updating the function name as you suggested does allow the fieldtype to install successfully, but it still doesn't work right. The fieldtype loads in the entry, but when you put in any address information and hit "Geocode Entry" it yields no results. That's why it was suggested to hack the fieldtype code. Like you, I do not recommend a system hack ever, so I am trying to find the portion of the add-on that EE 2.7+ does not like.
I've never built an add-on, so I am at a loss for where to go from here.