Can I create a Picker of Process Models?

Not sure the use case but Appian's Decisions feature may help, as PM can be an output. So, you could pick something else that results in PM selection.

Appian object output types - Decisions can return Appian objects as outputs which enables uses cases such as determining task assignment and dynamic process execution.

docs.appian.com/.../Appian_Decisions.html

Not sure the use case but Appian's Decisions feature may help, as PM can be an output. So, you could pick something else that results in PM selection.

Appian object output types - Decisions can return Appian objects as outputs which enables uses cases such as determining task assignment and dynamic process execution.

docs.appian.com/.../Appian_Decisions.html