Hi @MoiraH, thanks for reassuring me that others still want this feature! Hopefully they'll get around to implementing it soon rather than later, but I do have to admit that I do enjoy the StudioLink functionality they implemented in the Affinity suite.
Now, as to your question regarding workarounds, I have two that sorta work in a bodge-like fashion:
For single lines of text (i.e., titling or shaping to fit finite characters on a single line to a certain area), Artistic Text gets the job done. To avoid distortion, lock the aspect ratio before changing the size parameters in Transform palette).
For paragraphs of text, I tend to rely on the fact that you can change the font size by scrolling over the font size field in the toolbar. So, set the text frame size to what you want it to be, then adjust the font as necessary to desired size without overflowing by scrolling up/down to increase/decrease the size. (I think this works with linked frames as well, though I haven't done that recently.)
While these aren't quite as automated as the AutoFit Frame option in PagePlus, it works well enough to not be a complete blocker.
Hope this helps you out.