Objectives

Retain existing players when Chaos Legion rotates into Wild format, especially if they only own lower-level Chaos Legion cards. If players keep playing, they may rent or buy newer cards eventually.
Maintain utility for Chaos Legion cards and possibly other wild format cards. New players could buy Chaos Legion cards at this stage, knowing they could still play them casually in Wild format.
Increase/maintain demand for lower-level Chaos Legion & Wild cards.
Straightforward to implement.
Does not add significant complexity to the management of TOS violations.
It would allow continued usage of the one-click rental system, which would likely end when Chaos Legion rotates into Wild. The limited supply of both RB & CA plus conflict wagons would result in very few one-click rentals being available for modern from that time.
If a new player buys low-level Wild cards by accident, they can still use them in ranked.

Specification

Provide an option in Wild for players to play manually without incurring the season pass.
For any bot usage in Wild at all, the season pass would need to be paid in full before botting is permitted.
Botting providers would need to be notified of the change so they don't accidentally break TOS.

Implementation could be delayed until the day Chaos Legion rotates out of Modern format to avoid a reduction in match liquidity in the short term.
The low prices of Chaos Legion have created a number of problems, one of the major ones being the miss-management of player expectations that currently own a maxed CL deck. Many of these people can't afford maxed RB or CA, but would see little point in adding bronze-level cards to their collections, so they reach an impasse. Many will also be good players and bronze/silver level would not give the same level of complexity that they enjoy currently. We have the option to just let them continue playing their cards.
One critique of this is that some people want to force players to buy CA packs and cards when Chaos Legion rotates. However, I don't see that approach playing out well. People will only buy if they think it's worthwhile and the increased rewards in modern that we see should be that draw. Trying to force people would likely result in a lot of players just leaving the game and/or dropping the playing habit instead.