jeez ya those are restrictions, you got me on that, forgot about all of those.
Yeah... Previous editions where big on restrictions. No such thing as a neutral or evil paladin. Lawful good is the only way to go. The choices you get as a paladin in kingmaker screwed you if you didn't use the crappy lawful good choice and made you lose your powers. They had to slap a bandaid to soft fix it by adding in scrolls of atonement. I think back on 1e & 2e you could only be good aligned if you wanted to be a ranger.
5e fix that by leaving that up to your subclass. As for cleric you get abilities based on your domain that you picked along with bonus spells. Like the Arcana Domain gives you access to some of the Wizard spells with use of your wisdom modifier.
5th ed doesent have much restrictions at all honestly. Paladins can still lose their powers but how is kind of left up to the DM. That said the class itself does say that at page 86 that a Paladin who breaks his bow willingly and does not seak repentance could lose his class benefits or have to serve pentance somehow. Its left up to the DM though like alot of things are in DND.
Clerics domain spells are nice in that they are often spells that clerics normally dont have acces to. A light cleric can cast fireball for example and a tempest domain can cast lighnting bolt. Not huge things in itself but just small things that just denote themselves to be slightly different from clerics devoted to another domain.
Imho the channel divinity features are a bigger difference between clerics but that alone is also a small thing to differentiate clerics from eachother.
Aside from maybe a visual change by giving you stylized armor or something im not sure what they could alter. I dont think WOTC will want them to change class features
