Oh, my. I'm a big fan of today's theme. I had no idea what was going on. At first I thought the theme answers were just examples of phrases with repeated first syllables. But then I hit the revealer at 67A: Series whose first seven members are sung to the starts of 18-, 26-, 41- and 54-Across (ALPHABET).
See, if you use solfeggio to interpret those first syllables, you get C-C-G-G-A-A-G, which is the tune for the Alphabet Song (for A through G). Or, if you're a little more into foreign folk music, it's the French song "Ah, vous dirai-je, Maman," which Mozart wrote a lovely little set of variations on.
So I love the concept. LALALAND (great clue) and SOHELPMEGOD are solid answers. I can accept DODOBIRD I suppose, although I think the last word is redundantly extra. SOSOREVIEWS is definitely an ad hoc answer. It fits the purpose of the theme, but it is not a typical phrase. It fails the Google test miserably. Anyway, I'm ready to overlook the awkwardness.
BASSI is a nice addition to the theme. But how about TNOTE? Maybe if you found it in a SARONG you were singing. Too soon?
48A: Podded plants (OKRAS) jazzed up a bit of crosswordese. I also liked the clue at 69A: To eat a late lunch or wait until dinner, say (DILEMMA). And here's to the wonderful JODIE Whittaker, the new Doctor Who. She was outstanding in Broadchurch, and I have no doubt she'll do a great job in her new role.