v[count]B

.vimrc

" v[count]iBの逆版
vnoremap B :<C-u>call <SID>vNiB(v:count)<CR>

function! s:vNiB(count) range
  let l:n = max([1, s:blocklevel()-a:count])
  execute 'normal! v'.l:n.'iB'
endfunction

function! s:blocklevel() range
  " NOTE: getposの更新
  execute "normal! v\<ESC>"
  let l:start = s:get_position()

  let l:level = 0
  while 1
    let l:next = s:get_NiB_position(l:level + 1)
    if l:next.eq(l:start)
      break
    endif

    let l:level += 1
  endwhile

  return l:level
endfunction

function! s:get_NiB_position(N)
  let l:winview = winsaveview()
  
  execute 'normal! v'
  execute 'silent! normal '.a:N.'iB'
  execute "normal! \<ESC>"
  let l:ret = s:get_position()

  call winrestview(l:winview)
  return l:ret
endfunction

function! s:get_position()
  let l:pos = {
    \ 'start': getpos("'<")[1:2],
    \ 'end': getpos("'>")[1:2],
    \ }
  function! l:pos.eq(o)
    return self['start'] == a:o['start'] && self['end'] == a:o['end']
  endfunction
  
  return l:pos
endfunction