TMS Scripter is already cross-platform with the scripting engine, and it also can run FNX forms. However, the IDE and its visual components (form designer, object inspector) are VCL-only and there are no short-term plans to migrate them to FMX.
TMS Workflow Studio is VCL-only and there are no plans whatsoever to migrate it to FMX. We're working on an initial project that is a complete rewrite of the BPM engine to be cross-platform and server enabled, the (very) initial stage is available here: https://github.com/wlandgraf/octopus-bpm
Diagram Studio is a 100% VCL product and cannot be used in TMS WEB Core. There are a lot of similarities between TMS FNC Blox and TMS Diagram Studio but products do not have feature parity nor file compatibility. TMS FNC Blox was created & designed from the ground up for cross-platform, including web support and therefore several changes were needed to achieve this.