Heartstrings - An AWESOME name! I know that it got added on to "Lyra", which is an okay name, but let's all pause and appreciate just how good this name is on its own. First, it's part of an idiom ("playing on their heartstrings") instead of just being two random words jammed together. Second, it cleverly references the lyre being a stringed instrument. Perfect name.
Coloratura - Another great name! A colorataura is *looks at Dictionary.com* "an elaborate ornamentation of a vocal melody, especially in operatic singing by a soprano". But also it invokes the word "color". Both of those fit in perfectly with the pony's symbol--a colorful rainbow of music notes.
Tempest Shadow - This a perfect, badass, edgelord name for an edgelord pony.
Princess Celestia & Princess Luna - Dignified and beautiful names, I love them. (I also like Cadence but not quite as much as these two.)
Sunset Shimmer / Starlight Glimmer - They're both foils for Twilight Sparkle and thus both have names that are reminiscent of hers. (celestial body + word for light). I find that satisfying, but beyond that they're just very pleasant names on their own. I rank Sunset Shimmer a little above Starlight Glimmer because Sunset's name is tailored more specifically to her design.
Rarity - Originally a G3 name, but whatever, the point is this is a great name. Reminds me of the classic G1 names like "Glory." And I actually think it fits G4 Rarity better than G3 Rarity. G3 Rarity seems more like a Skedoodle, based on personality.
Sea Swirl - Great name, if someone told me this was a G1 sea pony's name I would believe them.
Big Macintosh / Granny Smith - I put these together because they're both "apple pun" names. A cute idea for an apple-themed family.
I'm not super well-versed on the blind bag ponies, but I took a quick look through them . . .
Sassaflash - A clever play on sassafrass AND sassy AND flash (because her symbol is lightning bolts). This is clever!
Sugar Grape - Just sounds delicious.
Sweetcream Scoops - Usually I am not a huge fan of alliterative names, they're a bit cringey to me. But this one sounds so yummy, plus it actually makes sense instead of being two random words that happen to start with the same letter. *stares directly at Peachy Pie, Pearly Pie, and Pinkie Pie WHY DID THEY DO THIS THREE TIMES*