In the following example echo on will take effect after the end of the brackets context is reached:

@echo off
(
    echo on
    echo ##
)
echo $$

In order to "activate" echo on in a brackets context (including FOR and IF commands) you can use FOR /f macro :

@echo off
setlocal

:: echo on macro should followed by the command you want to execute with echo turned on
set "echo_on=echo on&for %%. in (.) do"

(
  %echo_on% echo ###
)