It could be handy to be able to share custom review forms: quite often a lot of work goes into creating them, and other journals either within the same install or in other installs might benefit from being able to use a previously-created form as a starting base. Two possible ways to handle this: 

1) allow custom review forms to be optionally made available to other journals within the same OJS install. There could be a "share" checkbox on the form listings page allowing this. 

2) create some sort of XML import/export functionality. This would allow journals on other sites to export/import review forms.