There are two issues with allowing Midcap Nifty F&O contracts right now.
- Low client-wise OI limits- Clientwise OI limit for an F&O contract is 5% of the total open interest. Since the total OI is low, the limit is set is less than 1 lot. We are working with the exchange to have this limit exempted temporarily to allow trading.
The other reason is very low liquidity which @Meher_Smaran has explained in this post.