plot_compare_evokeds(list_of_evokeds, picks='grad')

yields
RuntimeWarning: More than 6 channels, truncating title ...

Two suggested enhancements:

1. if picks is one of the standard types (eeg, mag, grad...) then the title should reflect the channel type, rather than trying to list all channel names
2. if specific channels are requested, the truncation should happen with an info message printed to the terminal, not a RuntimeWarning (admittedly subjective, but I think a warning seems too strong for a "we truncated your plot title" message)