If streets or utilities are not available at the boundary of the proposed subdivision, and if the Planning and Zoning Commission finds the extensions across undeveloped areas would not be warranted as a special assessment to the intervening properties or as a municipal expense until some future time, the subdivider may be required, prior to approval of the final play, to obtain necessary easements or rights of way and construct and pay for such extensions. Such improvements shall be available for connections by subdividers of adjoining land.