Provision SPFx (.sppkg) add-ins on a site on-premise
ALM API is available now for SPO. SPFx now is available for SP2016 on-prem, too, since Feature Pack 2. But still there is no way to provision .sppkg files (either form local disk or from AppCatalog) on a site. Please, add this. There is no migration path from provider-hosted add-ins to SPFx add-ins for our applications now, because method LoadAndInstallApp() which worked for .app files does not work for .sppkg files.
Gašper Rupnik commented
You can already provision SPFx (.sppkg) packages to on-prem SharePoint Server 2016 -> here is solution https://rasper87.wordpress.com/2018/04/26/provision-spfx-web-parts-to-classic-sites-part-3-install-spfx-web-part-to-sharepoint-site-web/
OK, let's combine the effort on one suggestion. Please, vote for https://sharepoint.uservoice.com/forums/329220-sharepoint-dev-platform/suggestions/34135741-enterprise-deployment-of-sharepoint-framework-apps
Matt Schuessler commented
To clarify: the suggestion is to include the ALM API in SP2016 on-prem (as Feature Pack 3, maybe).