Bliss by discoDSP is a Virtual Instrument Audio Plugin and an Audio Plugin Host and a Standalone Application for macOS, Windows and Linux. It functions as a VST Plugin, an Audio Units Plugin, a VST 3 Plugin and a Standalone Application. It can host VST Plugins.
I was quite interested in this as it crosses platforms. Sounds great, and the demo did nothing to dissuade me until I hit the zone editor. It's badly in need of an easier, more visual way to define velocity layers and keyboard zones.
Absolutely agree with you! Since Bliss can import .xrni from Redux you can use Redux for mappings. Free demo is unlimited and can export .xrni. The simplest but time-consuming way is creation/edition of .sfz in text editor.