Starting at 2nd level, you can attempt to cast any spell scroll you find, regardless of which spell lists it belongs to.
Maybe higher level?
This is very situational, they should have other stuff
Starting at 2nd level, when you successfully cast a wizard spell using a spell scroll, you roll an Intelligence saving throw to avoid consuming the scroll. The DC for this saving throw equals 15 + the spell's level.
I'm unsure about this, but I can't place whyThis one is also very situational
At 10th level, you add three additional spells of your choice to your spellbook. These spells can be from any spell list but count as wizard spells for you. Each of these spells must be of a level for which you have spell slots. Each time you gain a Wizard level, you can replace one of these spells with another from any spell list.
What, if any, limitations should this have? (ritual only, 5th-level or lower?)
Up it to four? Its just adding them to spellbook not preping them
Move to 6th level?
Should this be stronger or weaker than Bard's Magical Secrets? (it's for a subclass but is the focus of the subclasses)
Maybe this should be 6th level?
Starting at 10th level, you can learn spells from others. Choose a spell of 5th-level or lower from any spell list, and that you do not have in your spellbook already.
You follow the usual rules for copying a scroll into your spellbook, except that you don't require a scroll. Instead you must spend the entire duration within 15ft of a willing creature that knows the spell, or has it prepared for the whole duration. Once you have spent this time and money, you can prepare the spell just like your other spells.
You can copy a number of spells this way up to your Intelligence modifier. In order to copy a further spell this way, you must discard one of the previous spells you copied with this feature from your spellbook.
Starting at 14th level, you always have the spells granted by your Versatile Spell Pages feature prepared, but they don't count against the number of wizard spells you prepare.
Definitely not strong enough to be the only 14th level feature
Other ideas
Adv. on checks to read scrolls
Check to not consume a scroll
Enhance Versatile spell scrolls