This feature was added to the after patch 8.0.0724 (kudos for Ingo Karkat for reporting it).
Neovim, as of now, hasn't merged this patch. However, it implements TextYankPost, which allows you to hack a similar behavior, as it provides the type of operation, the register used and the contents that was copied to the register.
Taking that into consideration, the following code snippet would do what you are asking for:
function! s:better_operator_message()
let number = len(v:event['regcontents'])
if v:event['operator'] == 'c' || v:event['operator'] == 'd'
let message = number . ' fewer lines'
elseif v:event['operator'] == 'y'
let message = number . ' lines yanked'
else
return
endif
if v:event['regname'] != ''
let message = message . ' into register ' . v:event['regname']
endif
echom message
endfunction
set report=10000000000
augroup better_operator_message
autocmd!
autocmd TextYankPost * call <sid>better_operator_message()
augroup end
I've made this snippet available as a plugin, in case you're interested.