Generally,　mobility　management　(MM)　solutions　are　centralized,　which　means　only　one　entity　controls　the　mobility-related　tasks　of　mobile　nodes　connected　to　the　network.　However,　the　massive　number　of　users,　rapid　growth　in　the　network　traffic,　and　the　recent　developments　regarding　the　architecture　and　capability　of　5G　networks　forced　multiple　entities　to　perform　the　task　of　MM.　Similarly,　to　fulfill　the　demand　for　the　applications　at　the　time　of　handoff,　we　have　on-demand　MM　solutions.　These　solutions　are　designed　to　be　adoptable　to　various　service　delivery　use　cases　supported　by　future　networks.　In　addition,　they　also　have　power-saving　features　that　turn　them　off　automatically,　when　all　your　devices　are　fully　charged.　Owing　to　stated　features,　we　need　to　explore　on-demand　MM　solutions　and　these　solutions　can　provide　divergent　types　of　services　according　to　the　user＇s　demand.　Therefore,　in　this　paper,　the　importance　and　comparison　of　on-demand　MM　solutions　with　legacy　mechanisms　are　presented,　by　keeping　in　view　the　merits　and　constraints　of　their　contributions.　Furthermore,　the　significance　of　the　MM　as　a　service　(MMaaS)　model　is　discussed　in　detail,　which　is　used　for　the　on-demand　MM　mechanism.　In　this　model,　the　substantial　characteristics　of　the　granularity　of　services　are　also　elaborated,　which　are　intricately　tangled　with　the　adoptability,　extensibility,　and　power-saving　requirements　of　future　wireless　networks.　Finally,　we　discuss　the　challenges,　future　prospects,　and　application　areas　of　on-demand　MM　solutions　for　researchers　and　application　developers.