Most Mendix-developer use Scrum and story points to get some project metrics. No FPA tool is available, but the new Mendix SIG tool can monitor KPI's of the project.

You can consider writing your own tool with the Mendix SDK. You can measure the size of the microflows and the forms. You still need to do a lot of bookkeeping stuff.

An advanced Mendix developer can make good predictions of the estimated time to complete a project. The all-time project dynamics like scope-creep, changing specs during the project are not solved with FPA.