Are there any such federal restrictions of which I might be unaware?
Yes, Article II Section 1 Clauses 2-3 and Amendment 12 of the Constitution of United States of America.
Under the Supremacy Clause (Article VI, Clause 2) states are subordinate to Federal Law and Authority; but, where not defined, States has the right and power to determine their own laws and powers. This is the basis of "state's rights' as originally defined by James Madison in Federalist No. 44.
This means that States are constitutionally mandated to follow Article II, Section 1, Clause 3 (which defines the electoral college) and the 12th amendment (which amends the electoral college's voting process). Left at this, pursuant to state's rights, each state has the right to determine how they chose their Electors. But, Article II Section 1 Clause 2 explicitly delegates the choosing of Electors to state legislatures.
Further, are there any state-level roadblocks?
Yes; but, this varies state to state.
Voting Rights Act of 1965
As Michael noted in his answer, notably, the Voting Rights Act of 1965 explicitly regulates voting laws. Nationally, every state is prohibited from legislating racial discrimination, legislating literacy tests, and other devices historically used to discriminate against minority groups. The Act also provides "special provisions" that apply only to specified jurisdictions. In particular section 5 prohibits these jurisdictions from legislating any changes to their voter laws without preapproval from the US Attorney General or the US District court for D.C. to ensure the law will not impact protected minority groups. Furthermore, Section 4(f)(4) and Section 203(c) requires states with language minorities to provide multilingual or bilingual ballots. Note that the Voting Rights Act applies to the the states of Arizona, Texas, Alaska, Louisiana, Mississippi, Alabama, Georgia, South Carolina, and Virginia but also to ** jurisdictions**.
Resistance to Change
I don't have the time at the moment to provide cited evidence for this; but, whenever legislation is passed, it typically receives some resistance to change. Proponents of changing the voting system will receive resistance in the form of why change it? what we have already works! These opponents would provide some of your biggest roadblocks.
At the municipal level, the municipality must adhere to the state legislature's laws on voting. This is why you don't see municipal level laws regarding voting.