I am also surprised how challenging it often is to use both the original muse, and the muse S.
We are making an EEG headband for increasing the efficiency of deep sleep, and though we are still improving on our data reliability, using the right materials and structure, it can be much more reliable than Muse.
Earphone EEG already exists, they don't use "metal contacts", and neither do we. There are conductive silicones, and conductive fabrics which better conform to the skin and provide good signal quality and comfort.
However, they still don't work well with movement. This is the challenge I see with in-ear.
A neuroscientist I know just bought a pair of Emotiv MN8 (https://www.emotiv.com/mn8-eeg-headset-with-contour-app/) earbuds, and said they wanted to try it while running. I have serious doubts that will work, as all EGG is susceptible to movement noise.
But in ear silicone conductive tips while meditating, I think that will be fine. LGs I think are out this year, Emotiv already are, there are a few others as well.
The other alternative is fNIRS, which is more similar to an ECG monitor in your smartwatch. It is measuring bloodflow through the brain, but there is a delay between bloodflow and brain activity, so it was a non-starter for us as we are responding to your brain activity in real-time, but I think for meditation or similar uses it would be fine, and maybe even preferred.