Not really , if you are on the journey and have PR pre 20/4/17 and they have moved the goal posts what's to say they won't do it again, thereby never achieving citizenship , changes should only apply to new PR approvals .
The governemt went abroad to attract certain skills and made representations regarding the route to citizenship , some of these people were the most highly skilled in the world and could have gone to any country it's unreasonable to move the goals posts
also a visa is a visa it can be changed its highly unlikely but theoretically possibly all PR's would be cancelled. Not a good position to be in if you have a big asset base built up here.
also in a case I know the guy needs to travel to PNG weekly to develop his Australian business that employs Aussies , he spends 2-4 days a week in PNG, he will never comply with the minimum residency requirement if he does this so now has a choice to grow his Australian business and keep people employed in australia or obtain his citizenship , he's talking about closing the business and going back into employment as he wants citizenship asap for the security of assets etc thereby Australian 5people will loose their jobs .
Besides all all that the principle of moving The goal posts is unfair and not an Australian value , one of supposed reasons for the changes are to ensure Australian values
by all means make the changes it's their country but they should be grandfathered for this with PR