It isn't however, and I think for good reasons. First and foremost is the fact that the bill simply codifies what has been, via jurisprudence, the law of the land for some time now. Then there is the fact that over the course of the entire debate, public opinion has not changed at all; most people still prefer the traditional definition. The fact of this bill becoming law is not likely to change that.
It is likely that whatever changes do come about as a result of the passage of this legislation are likely to take years to be felt fully. Some things I can see happening:
1. Denominations in the free church tradition will experience splits or slips. There are already rumblings that rogue, or "free thinking" ministers will want to marry same sex couples, regardless of denominational beliefs or policy statements. This will test the resolve, internal discipline, and unity of several denominations. Either they will discipline the ministers and the congregations who want to head in that direction, meaning suspension of denominational credentials and membership, or they will compromise.
2. A large percentage of Christian denominations, if not of faith communities generally, will get out of the marriage business. Marriage ceremonies will be performed, but no longer will ministers register them for the government. That function is voluntary, and only matters if the couple wishes their marriage recognized by the government. There are favorable tax implications to not registering the marriage, and there is no legal obligation to do so, thus no issue of failing to submit to authorities is involved. Couples would be free to register their marriage so via a justice of the peace at their option in any case. Spousal benefits are not at risk since the government accepts all conjugal cohabitation arrangements as defacto common law marriages.
3. In fact getting out of the legal marriage business may be the only way for churches to avoid prosecution in the future. If marriage in churches is strictly a religious matter independent from, if parallel to, the legal institution, then it would seem impossible for churches to be sued for discrimination. It would simply be a matter of the church separating from the state, and removing itself from the state's jurisdiction. The state has no say on whom churches may baptize, so making marriage a purely religious ceremony should provide the church a similar jurisdictional hedge. Strange as it may sound, the best way for marriage to be preserved in the church may be for the church and state to amicably divorce over what can only be called irreconcilable differences on the point of the definition of marriage.
Of course it is more politically expedient to try to paint the opposition as a radical fringe that will go to the extreme.
That is an old tactic of the Liberals. In that regard, nothing has changed.