In your ~/.config/nvim/init.vim, have something like

function! TW_done(channel)
    call rpcrequest( a:channel, 'tw_done' )
endfunction

function! TW_show(...)
    if a:0
        call rpcrequest( g:nvimx_channel, 'tw_show', a:1 )
    else
        let filter = input( "filter: ", " " )
        call rpcrequest( g:nvimx_channel, 'tw_show', filter )
    endif

endfunction

function! TW_toggle_focus(channel)
    call rpcrequest( a:channel, 'tw_toggle_focus' )
endfunction

function! TW_mod(channel)
    call rpcrequest( a:channel, 'tw_mod' )
endfunction

au FileType task map <leader>d :call TW_done(nvimx_channel)<CR>
au FileType task map <leader>ll :call TW_show('+PENDING -WAITING -BLOCKED')<CR>
au FileType task map <leader>lq :call TW_show()<CR>
au FileType task map <leader>m :call TW_mod(nvimx_channel)<CR>
au FileType task map <leader>f :call TW_toggle_focus(nvimx_channel)<CR>
au FileType task map <buffer> <leader>ph :call TW_mod(nvimx_channel)<CR>

au FileType task set nowrap

" requires the plugin dhruvasagar/vim-table-mode
au FileType task TableModeEnable

then set the env variable NVIM_LISTEN_ADDRESS to, say, 127.0.0.1:6543 and start nvim in one shell, and this script in another, and enjoy your new nvim-powered taskwarrior UI!