Mod name
ViaFabric and multiconnect

Curseforge link
https://www.curseforge.com/minecraft/mc-mods/viafabric https://www.curseforge.com/minecraft/mc-mods/multiconnect

Modrinth link
N/A

Other link
https://github.com/ViaVersion/ViaFabric https://github.com/Earthcomputer/multiconnect

What it does
Both add support for playing old servers in new client and they complement each other with features

Why should it be in the modpack
So people can play on old servers with the modpack

Why shouldn't it be in the modpack
Server incompatibilities, AntiGhost incompatibility, potential bans on some servers, no way to completely opt out

Categories

• Performance optimization
• Graphics optimization
• New feature
• Optifine parity
• Fixes a bug/dependency

Additional details
Suggested on the listing though

• A bit too dangerous to add for everyone (as there is a risk of general rule-breaking or anti-cheat bans)
• multiconnect has a bit confusing UX, but ViaFabric has worse emulation
• Chance of glitches, e.g. swimming in water or crouching under 1.5 blocks
• Bad endorsement of playing old servers at all
• There are likely very few people who would bother using a new client with intentionally old servers anyway