I don't think so, I think this is for professional users. Grandma is not gonna realize that the slightly greyed out text is not already there, and also that tab actually writes out the text for her.

In my experience anything keyboard related is not a good solution for “grandma”. What I’ve seen work best is voice to text. My dad composes all of his messages with voice, as the alternative is first finding his reading glasses, then pecking out keys with only his index fingers at a rate of about half a key a second.

Sure he could abbreviate and autocomplete his way through a sentence... but then I’m not talking to my dad anymore; instead I’m talking to some k’th mean of human interaction.

Watch out. That's a stereotype, and it might be offensive.