An effort to put a solid taproot proposal was done by developer Anthony Towns, the proposal was about segwit v1 with several adjustments to the current segwit version which included :

• replacing the ECDSA Checksig/CheckMultiSign ops with new Schnorr ops
• introducing a 33-byte v1 witness addresses that encode a secp256k1 ECC Point P that is spendable either by a direct schnorr signature of a script with the witness data and a taproot/merkle path to the script.
• Versions for taproot scripts
• Adding OP_MASK to support script masking via sighash
• Making invalid opcodes upgradeable to have more flexibility than OP_NOP

read the proposal here