>There are many greatly conservative IE languages alive today, including Lithuanian, most Slavic languages, and Icelandic.
It does not matter how much a 'language can be conservative', if it's using too much symbols, or symbols that are not popular it will always be a ruin.
Chynese. Rus'. Gryk. And so on.
I see one possibility: the only symbols that a modern, realistic language can use are the ones from the core Latin alphabet.