The most obvious two changes would be:

• disallow 0 as a juxtaposed numeric literal coefficient: 0n would be a syntax error.
• disallow juxtaposition of floating-point numeric literals with trailing .: 1.x would be a syntax error.

There may be others but these two strike me as clearly a good idea. One nice thing about disallowing 0 as a juxtaposed numeric literal coefficient is that it opens up as many 0x1234 syntaxes as one might ever want, so it kind of future-proofs us for that. Another nice thing is that instead of getting a surprise when they try 0x after 0y just working, people will get a warning as soon as they try 0y and they can immediately learn that 0 doesn't work as a juxtaposed numeric literal coefficient.