This is a recent directive from CASA, that pilots wishing to perform owner maintenance must pass a test to qualify for a L1 maintenance authority - which previously was automatic. Most members I'm sure would agree that our basic pilot training is not adequate preparation on its own for aircraft owners to perform whatever maintenance their aircraft may require. So on that basis this is a sensible move.
There are several groups of RA-Aus pilots when it comes to maintenance. The majority don't own an aircraft and don't need an L1 maintenance authority. A second group don't want to maintain their aircraft themselves and are happy to pay an L2 to do it - they also don't need an L1 maintenance authority. A third group do want to maintain their aircraft, have the necessary expertise and do it just fine. This group will need an L1 maintenance authority and it should be a formality to get one - just pass an online test. The fourth group want to maintain their aircraft but don't have the expertise. Some of them also don't recognise this. This is the group we need to target and the only way to identify them is to test everyone who wants to do owner maintenance.
Note the distinction between owner maintenance and pilot maintenance. All pilots will continue to have the authority to perform pilot maintenance - the same tasks GA pilots can perform including topping up fluids, fixing a flat tyre, etc. An L1 authority (or higher) will be required to perform owner maintenance - which could include changing the prop, engine repairs, airframe repairs, electrical work, etc.
Note also that all maintenance authorities (L1, L2, etc.) are limited to those tasks for which the authority holder is competent. For example, if you have an L1 but you don't know what a torque wrench is, you are not authorised to pull the heads off your engine since a torque wrench is an essential tool for that task. Once you learn what a torque wrench is and how to use one, you may be authorised provided you are competent in all the other steps involved in the task. Determining competency to that degree is up to the individual, and the responsibility will be on the individual if anything goes wrong.
Final note, nothing has changed in relation to aircraft used for flight training or hire. Those aircraft still must be maintained by the holder of an L2 (or higher) maintenance authority.