If you haven't noticed the Reference Panel option in Dynamics 365 CE then take a look. Reference Panels can render Sub grids in one section through the Unified Interface (UCI). It does this by providing tab buttons for users to navigate between them. This makes for a very nice user experience and cleans up the clutter on the form.
Posts published in “Dynamics 365”
Microsoft has released native embedding of Canvas Apps into Dynamics 365 forms. I believe this will change the way we implement solution for clients. It will allow bringing together of more data sources to the user via Microsoft Flow. The release is slowing rolling out the regions which includes Australia, Canada, India, or Japan as of December 2018. Most regions will have the functionality in January.
The link to the recent post is here: https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/embed-canvas-app-in-form
To utilise the new feature in Dynamics 365 simply add a field or subgrid to the form. Via the change properties, under the controls tab a new Canvas App control is available.
I recently spun up a trial to check out the new feature and played around creating a simple embedded canvas app on the contact form.