The tools that will help you to work on scriptlets in the future are those that will shape the evolution of scriptlets. In our opinion, topics such as licensing and protection might become a central issue, if scriptlets are to succeed in populating both Web pages and Windows 9x folders. If scriptlets really succeed in becoming standard reusable components, then they must be safely and easily distributable. So a first absolute necessity will be for a compiler in order to produce non-human readable code. This will also allow you to hide licensing or signing information somewhere. Then you might need a packager, able to inform you of all the dependencies of the scriptlet and write down a setup cabinet file. Finally, you might want an editor with some facilities such as a few wizards and toolbars for specific tasks such as inserting certain tags. More, you might expect the IntelliSense support, encompassing all the features of VB5 such as word auto-completion, properties and methods suggestions, tooltips and more- all of which will be available in Visual InterDev 2.0.
As for authoring tools that use scriptlets, what is needed is just an enhanced version of FrontPage's and ActiveX Control Pad's ScriptWizard and a dialog that allows you to pick up and insert scriptlets inside DHTML documents.