So if SharePoint Designer 2013 will be the latest version that Microsoft will be supporting/releasing; any ideas as of what would be replacing SP Designer? I know you can still use SP 2013 64bit with SP 2016 but I'm curious.
You are right, InfoPath 2013 and SharePoint Designer 2013 will be the last versions of those products meanwhile Microsoft will continue to support custom workflows built with SharePoint Designer and hosted on SharePoint Server 2016 and Office 365.
You should also be aware of the support for InfoPath 2013 and SharePoint Designer 2013 will match the support life cycle for SharePoint Server 2016, running until 2026.
Untile now Microsoft hasn't announced for an explicit alternative for SharePoint Designer.But in SharePoint Online there is PowerApps
- PowerApps is a service for building and using custom business apps that connect to your data and work across the web and mobile – without the time and expense of custom software development.
- PowerApps also introduce a logic Flow to create automated workflows between your favorite apps and services to get notifications, synchronize files, collect data, and more.
As you know you can still use the Sharepoint designer for 2016, because code base for sharepoint 2013 and 2016 is same.
MSFT discouraging us to use SPD for customization rather they recommend us to us the scripting.
As an alternate, mostly people use designer for workflows, you can use power apps or Microsoft flow for it. You can still use visual studio for wf.
For designing you can use dream-viewer.
Indeed, you can use also PowerApps as an alternative for SPD (it's also the Microsoft family), or consider other options, 3rd party vendors like Nintex, K2 or WEBCON BPS. They are all low-code platforms which enable creating workflows. Keep in mind that both Nintex and K2 offer separate products for workflow and forms while WEBCON BPS has them both in one.