A proposed merger between Sky and Vodafone was declined by the Commerce Commission this year.
NZR's bargaining power will increase if Spark and TVNZ come to the negotiating table, especially if conglomerate Amazon remain interested via their Prime Video streaming service.
In September, the Weekend Herald reported the bidding process would start earlier than usual - in April next year - so Amazon could address infrastructural issues like New Zealand's broadband speed.
The story suggested rights could be divvied between Sky and any challengers, meaning Amazon could cherry-pick games rather than take on full-scale production, or NZR could produce some elements in-house.
The most recent research from investment broking firm Forsyth Barr suggested Sky "faces considerable disruptive forces with escalating competition for both audiences and content. We expect a slow medium-term revenue bleed from subscriber attrition, customers trimming bundles and declining advertising revenue, with higher content costs a material longer-term threat".
If Spark and TVNZ mounted a challenge it could expect to find favour within the coalition government.
New Zealand First's manifesto includes a policy that games of national significance be broadcast free-to-air.
The concern about making that a reality is many professional sports are funded through broadcasting rights. Any successful bidder would need recompensing for any estimated loss in revenue if legislation is put in place to guarantee free-to-air coverage.
Using sport to win an audience share and advertising revenue can work well for free-to-air television networks. As an example, Channel Nine have created an annual cash cow in Australia through their international cricket coverage, albeit to a bigger population.
From a digital platform perspective, Spark can take heart that BT (formerly British Telecommunications PLC) has acquired the rights to the 2017-18 Ashes.
On the flipside, if Sky were to lose premium content such as rugby rights, the loss in subscribers could have a compounding effect on delivering profit to shareholders.
However, Sky still appear to be the company best-resourced to broadcast local rugby matches through their production arm and their intimate knowledge of the New Zealand live sports broadcasting scene.