"I can still file my trading income under 44AD for AY 2018-19. Right?"
Yes, I am of the same opinion.
"I have heard rumours that IT Department has banned traders from opting 44AD."
No such official announcement/notification.
Only point is once you have opted out from Sec. 44AD, you have to keep books and get them audited for next FIVE years, and can't opt in till such period.
The 'Business Code' to be used in case of 'Stock Market Intraday / FnO Trading activities
No specific code allotted till now, but can apply......
09028-Retail sale of other products n.e.c ......for time being...